[8] p. 11.—“Traditions of Samothrace.”
Diodorus has preserved to us this remarkable tradition, the probability of which renders it in the eyes of the geologist almost equivalent to a historical certainty. The Island of Samothrace, formerly called also Æthiopea, Dardania, Leucania or Leucosia in the Scholiast to Apollonius Rhodius, and which was a seat of the ancient mysteries of the Cabiri, was inhabited by the remains of an ancient nation, several words of whose language were preserved to a later period in the ceremonies accompanying sacrifices. The situation of this island, opposite to the Thracian Hebrus and near the Dardanelles, renders it not surprising that a more detailed tradition of the catastrophe of the breaking forth of the waters of the Euxine should have been preserved there. Rites were performed at altars supposed to mark the limits of the irruption of the waves; and in Samothrace as well as in Bœotia, a belief in the periodically recurring destruction of mankind, (a belief which was also found among the Mexicans in the form of a myth of four destructions of the world), was connected with historical recollections of particular inundations. (Otfr. Müller Geschichten Hellenischer Stämme und Städte, Bd. i. S. 65 and 119.) According to Diodorus, the Samothracians related that the Black Sea had once been an inland lake, but that, being swollen by the rivers which flow into it, it had broken through, first the strait of the Bosphorus, and afterwards that of the Hellespont; and this long before the inundations spoken of by other nations. (Diod. Sicul. lib. v. cap. 47, p. 369, Wesseling.) These ancient revolutions of nature have been treated of in a special work by Dureau de la Malle, and all the information possessed on the subject has been collected in Carl von Hoff’s important work, entitled Geschichte der natürlichen Veränderungen der Erdoberfläche, Th. i. 1822, S. 105-162; and in Creuzer’s Symbolik, 2te Aufl. Th. ii. S. 285, 318, and 361. A reflex, as it were, of the traditions of Samothrace appears in the “Sluice theory” of Strato of Lampsacus, according to which the swelling of the waters of the Euxine first opened the passage of the Dardanelles, and afterwards caused the outlet through the pillars of Hercules. Strabo has preserved to us in the first book of his Geography, among critical extracts from the works of Eratosthenes, a remarkable fragment of the lost writings of Strato, presenting views which extend to almost the entire circumference of the Mediterranean.
“Strato of Lampsacus,” says Strabo (Lib. i. p. 49 and 50, Casaub.), “is even more disposed than the Lydian Xanthus,” (who had described impressions of shells at a distance from the sea) “to expound the causes of the things which we see. He asserts that the Euxine had formerly no outlet at Byzantium, but the sea becoming swollen by the rivers which ran into it, had by its pressure opened the passage through which the waters flow into the Propontis and the Hellespont. He also says that the same thing has happened to our Sea (the Mediterranean);” “for here, too, when the sea had become swollen by the rivers, (which in flowing into it had left dry their marshy banks), it forced for itself a passage through the isthmus of land connecting the Pillars. The proofs which Strato gives of this are, first that there is still a bank under water running from Europe to Libya, shewing that the outer and inner seas were formerly divided; and next that the Euxine is the shallowest, the Cretan, Sicilian, and Sardoic Seas being on the contrary very deep; the reason being that the Euxine has been filled with mud by the many and large rivers flowing into it from the North, while the other seas continued deep. The Euxine is also the freshest, and the waters flow towards the parts where the bottom of the sea is lowest. Hence he inferred that the whole of the Euxine would finally be choked with mud if the rivers were to continue to flow into it: and this is already in some degree the case on the west side of the Euxine towards Salmydessus (the Thracian Apollonia), and at what are called by mariners the “Breasts” off the mouth of the Ister and along the shore of the Scythian Desert. Perhaps the Temple of Ammon (in Lybia) may once have stood on the sea-shore, and causes such as these may explain why it is now far inland. This Strato thought might account for the celebrity of the Oracle, which would be less surprising if it had been on the sea-shore; whereas its great distance from the coast made its present renown inexplicable. Egypt, too, had been formerly overflowed by the sea as far as the marshes of Pelusium, Mount Casius, and Lake Serbonis; for, on digging beneath the surface, beds of sea-sand and shells are found; shewing that the country was formerly overflowed, and the whole district round Mount Casius and Gerrha was a marshy sea which joined the gulf of the Red Sea. When our Sea (the Mediterranean) retreated, the land was uncovered; still, however, leaving the Lake of Serbonis: subsequently this lake also broke through its bounds and the water flowed off, so that the lake became a swamp. The banks of Lake Mœris are also more like sea than river banks.” An erroneously corrected reading introduced by Grosskurd on account of a passage in Strabo, Lib. xvii. p. 809, Cas., gives instead of Mœris “the Lake Halmyris:” but this latter lake was situated not far from the mouth of the Danube.
The sluice-theory of Strato led Eratosthenes of Cyrene (the most celebrated of the series of librarians of Alexandria, but less happy than Archimedes in writing on floating bodies), to examine the problem of the equality of level of all external seas, i. e., seas surrounding the Continents. (Strabo, Lib. i. p. 51-56; Lib. ii. p. 104, Casaub). The varied outlines of the northern shores of the Mediterranean, and the articulated form of the peninsulas and islands, had given occasion to the geognostical myth of the ancient land of Lyctonia. The supposed mode of origin of the smaller Syrtis and of the Triton Lake (Diod. iii. 53-55) as well as that of the whole Western Atlas (Maximus Tyrius, viii. 7) were drawn in to form part of an imaginary scheme of igneous eruptions and earthquakes. (See my Examen crit. de l’hist. de la Géographie, Vol. i. p. 179; T. iii. p. 136.) I have recently touched more in detail on this subject (Kosmos, Bd. ii. S. 153; Engl. ed. p. 118-119) in a passage which I permit myself to subjoin:—
A more richly varied and broken outline gives to the northern shore of the Mediterranean an advantage over the southern or Lybian shore, which according to Strabo was remarked by Eratosthenes. The three great peninsulas, the Iberian, the Italian, and the Hellenic, with their sinuous and deeply indented shores, form, in combination with the neighbouring islands and opposite coasts, many straits and isthmuses. The configuration of the continent and the islands, the latter either severed from the main or volcanically elevated in lines, as if over long fissures, early led to geognostical views respecting eruptions, terrestrial revolutions, and overpourings of the swollen higher seas into those which were lower. The Euxine, the Dardanelles, the Straits of Gades, and the Mediterranean with its many islands, were well fitted to give rise to the view of such a system of sluices. The Orphic Argonaut, who probably wrote in Christian times, wove antique legends into his song; he describes the breaking up of the ancient Lyktonia into several islands, when ‘the dark-haired Poseidon, being wroth with Father Kronion, smote Lyktonia with the golden trident.’ Similar phantasies, which indeed may often have arisen from imperfect knowledge of geographical circumstances, proceeded from the Alexandrian school, where erudition abounded, and a strong predilection was felt for antique legends. It is not necessary to determine here whether the myth of the Atlantis broken into fragments should be regarded as a distant and western reflex of that of Lyktonia (as I think I have elsewhere shewn to be probable), or whether, as Otfried Müller considers, “the destruction of Lyktonia (Leuconia) refers to the Samothracian tradition of a great flood which had changed the form of that district.”
[9] p. 12.—“Prevents precipitation taking place from clouds.”
The vertically-ascending current of the atmosphere is a principal cause of many most important meteorological phenomena. When a desert or a sandy plain partly or entirely destitute of plants is bounded by a chain of high mountains, we see the sea breeze drive the dense clouds over the desert without any precipitation taking place before they have reached the mountain-ridge. This phenomenon was formerly explained in a very inappropriate manner by a supposed superior attraction exercised by the mountains on the clouds. The true reason of the phenomenon appears to consist in the ascending column of warm air which rises from the sandy plain, and prevents the vesicles of vapour from being dissolved. The more complete the absence of vegetation, and the more the sand is heated, the greater is the height of the clouds, and the less can any fall of rain take place. When the clouds reach the mountains these causes cease to operate; the play of the vertically-ascending atmospheric current is feebler, the clouds sink lower, and dissolve in rain in a cooler stratum of air. Thus, in deserts, the want of rain, and the absence of vegetation, act and react upon each other. It does not rain, because the naked sandy surface having no vegetable covering, becomes more powerfully heated by the solar rays, and thus radiates more heat; and the absence of rain forbids the desert being converted into a steppe or grassy plain, because without water no organic development is possible.
[10] p. 14.—“The mass of the earth in solidifying and parting with its heat.”
If, according to the hypothesis of the Neptunists, now long since obsolete, the so-called primitive rocks were precipitated from a fluid, the transition of the crust of the earth from a fluid to a solid state must have been accompanied by an enormous disengagement of heat, which would in turn have caused fresh evaporation and fresh precipitations. The later these precipitations, the more rapid, tumultuous, and uncrystalline they would have been. Such a sudden disengagement of heat might cause local augmentations of temperature independent of the height of the pole or the latitude of the place, and independent of the position of the earth’s axis; and the temperatures thus caused would influence the distribution of plants. The same sudden disengagement of heat might also occasion a species of porosity, of which there seem to be indications in many enigmatical geological phenomena in sedimentary rocks. I have developed these conjectures in detail in a small memoir “über ursprungliche Porosität.” (See my work entitled Versuche über die chemische Zersetzung des Luftkreises, 1799, S. 177; and Moll’s Jahrbücher der Berg- und Hüttenkunde, 1797, S. 234.) According to the newer views which I now entertain, the shattered and fissured earth, with her molten interior, may long have maintained a high temperature on her oxydised surface, independently of position in respect to the sun and of latitude. Would not the climate of Germany be wonderfully altered, and that perhaps for centuries, if there were opened a fissure a thousand fathoms in depth, reaching from the shores of the Adriatic to the Baltic? If in the present condition of our planet, the stable equilibrium of temperature, first calculated by Fourier in his Théorie analytique de la chaleur, has been almost completely restored by radiation from the earth into space; and if the external atmosphere now only communicates with the molten interior through the inconsiderable openings of a few volcanoes,—in the earlier state of things numerous clefts and fissures, produced by the frequently recurring corrugations of the rocky strata of the globe, emitted streams of heated air which mingled with the atmosphere and were entirely independent of latitude. Every planet must thus in its earliest condition have for a time determined its own temperature, which afterwards becomes dependent on the position relatively to the central body, the Sun. The surface of the Moon also shows traces of this reaction of the interior upon the crust.
[11] p. 14.—“The mountain declivities of the southern part of Mexico.”
The greenstone in globular concretions of the mountain district of Guanaxuato is quite similar to that of the Franconian Fichtel-Gebirge. Both form grotesquely shaped summits, which pierce through and cover the transition argillaceous schists. In the same manner, pearl stone, porphyritic schists, trachyte, and pitch-stone porphyry, constitute rocks similar in form in the Mexican mountains near Cinapecuaro and Moran, in Hungary, in Bohemia, and in Northern Asia.
[12] p. 16.—“The dragon-tree of Orotava.”
This colossal dragon-tree, Dracæna draco, stands in the garden of Dr. Franqui in the small town of Oratava, the ancient Taoro, one of the most delightful spots in the world. In June 1799, when we ascended the Peak of Teneriffe, we measured the circumference of the tree, and found it nearly 48 English feet. Our measurement was taken several feet above the root. Lower down, and nearer to the ground, Le Dru made it nearly 79 English feet. Sir George Staunton found the diameter still as much as 12 feet at the height of 10 feet above the ground. The height of the tree is not much above 69 English feet. According to tradition, this tree was venerated by the Guanches (as was the ash-tree of Ephesus by the Greeks, or as the Lydian plane-tree which Xerxes decked with ornaments, and the sacred Banyan-tree of Ceylon), and at the time of the first expedition of the Béthencourts in 1402, it was already as thick and as hollow as it now is. Remembering that the Dracæna grows extremely slowly, we are led to infer the high antiquity of the tree of Orotava. Bertholet, in his description of Teneriffe, says, “En comparant les jeunes Dragonniers, voisins de l’arbre gigantesque, les calculs qu’on fait sur l’age de ce dernier effraient l’imagination.” (Nova Acta Acad. Leop. Carol. Naturæ Curiosorum, T. xiii. 1827, p. 781.) The dragon-tree has been cultivated in the Canaries, and in Madeira and Porto Santo, from the earliest times; and an accurate observer, Leopold von Buch, has even found it wild in Teneriffe, near Igueste. Its original country, therefore, is not India, as had long been believed; nor does its appearance in the Canaries contradict the opinion of those who regard the Guanches as having been an isolated Atlantic nation without intercourse with African or Asiatic nations. The form of the Dracænas is repeated at the southern extremity of Africa, in the Isle of Bourbon, and in New Zealand. In all these distant regions species of the genus in question are found, but none have been met with in the New Continent, where its form is replaced by that of the Yucca. Dracæna borealis of Aiton is a true Convallaria, and has all the “habitus” of that genus. (Humboldt, Rel. hist. T. i. p. 118 and 639.) I have given a representation of the dragon-tree of Orotava, taken from a drawing made by F. d’Ozonne in 1776, in the last plate of the Picturesque Atlas of my American journey. (Vues des Cordillères et Monumens des Peuples indigènes de l’Amérique, Pl. lxix.) I found d’Ozonne’s drawing among the manuscripts left by the celebrated Borda, in the still unprinted travelling journal entrusted to me by the Dépôt de la Marine, and from which I borrowed important astronomically-determined geographical, as well as barometric and trigonometric notices. (Rel. hist. T. i. p. 282.) The measurement of the dragon-tree of the Villa Franqui was made on Borda’s first voyage with Pingré, in 1771; not in his second voyage, in 1776, with Varela. It is affirmed that in the early times of the Norman and Spanish Conquests, in the 15th century, Mass was said at a small altar erected in the hollow trunk of the tree. Unfortunately the dragon-tree of Orotava lost one side of its top in the storm of the 21st of July, 1819. There is a fine and large English copperplate engraving which represents the present state of the tree with remarkable truth to nature.
The monumental character of these colossal living vegetable forms, and the kind of reverence which has been felt for them among all nations, have occasioned in modern times the bestowal of greater care in the numerical determination of their age and the size of their trunks. The results of these inquiries have led the author of the important treatise, “De la longévité des Arbres,” the elder Decandolle, Endlicher, Unger, and other able botanists, to consider it not improbable that the age of several individual trees which are still alive goes back to the earliest historical periods, if not of Egypt, at least of Greece and Italy. It is said in the Bibliothèque Universelle de Genève, 1831, T. lxvii. p. 50:—“Plusieurs exemples semblent confirmer l’idée qu’il existe encore sur le globe des arbres d’une antiquité prodigieuse, et peut-être témoins de ses dernières révolutions physiques. Lorsqu’on regarde un arbre comme un agrégat d’autant d’individus soudés ensemble qu’il s’est développé de bourgeons à sa surface, on ne peut pas s’étonner si, de nouveaux bourgeons s’ajoutant sans cesse aux anciens, l’agrégat qui en résulte n’a point de terme nécessaire à son existence.” In the same manner Agardh says:—“If in trees there are produced in each solar year new parts, so that the older hardened parts are replaced by new ones capable of conducting sap, we see herein a type of growth limited only by external causes.” He ascribes the shortness of the life of herbs, or of such plants as are not trees, “to the preponderance of the production of flowers and fruit over the formation of leaves.” Unfruitfulness is to a plant a prolongation of life. Endlicher cites the example of a plant of Medicago sativa, var. β versicolor, which, bearing no fruit, lived eighty years. (Grundzüge der Botanik, 1843, S. 1003).
With the dragon trees, which, notwithstanding the gigantic development of their closed vascular bundles, must by reason of their floral parts be placed in the same natural family with asparagus and garden onions, we must associate the Adansonia (monkey bread-tree, Baobab,) as being certainly among the largest and oldest inhabitants of our planet. In the very first voyages of discovery of the Catalans and Portuguese, the navigators were accustomed to cut their names on these two species of trees, not merely to gratify the desire of handing down their names, but also to serve as marks or signs of possession, and of whatever rights nations claim on the ground of being the first discoverers. The Portuguese navigators often used as their “marco” or token of possession the French motto of the Infant Don Henrique the Discoverer. Manuel de Faria y Sousa says in his Asia Portuguesa (T. i. cap. 2, pp. 14 and 18):—“Era uso de los primeros Navegantes de dexar inscrito el Motto del Infante, talent de bien faire, en la corteza de los arboles.” (Compare also Barros, Asia, Dec. I. liv. ii. cap. 2, T. i. p. 148; Lisboa, 1778.)
The above-named motto cut on the bark of two trees by Portuguese navigators in 1435, twenty-eight years therefore before the death of the Infante, is curiously connected in the history of discoveries with the elucidations to which the comparison of Vespucci’s fourth voyage with that of Gonzalo Coelho, in 1503, has given rise. Vespucci relates that Coelho’s admiral’s ship was wrecked on an island which has been sometimes supposed to be San Fernando Noronha, sometimes the Peñedo de San Pedro, and sometimes the problematical Island of St. Matthew. This last-named island was discovered by Garcia Jofre de Loaysa on the 15th of October, 1525, in 2½° S. lat., in the meridian of Cape Palmas, almost in the Gulf of Guinea. He remained there eighteen days at anchor, found crosses, as well as orange trees which had been planted and had become wild, and on two trunks of trees inscriptions dating back ninety years. (Navarrete, T. v. pp. 8, 247, and 401.) I have examined the questions presented by this account more in detail in my inquiries into the trustworthiness of Amerigo Vespucci. (Examen critique de l’hist. de la Geographie, T. v. pp. 129-132.)
The oldest description of the Baobab (Adansonia digitata), is that given by the Venetian Aloysius Cadamosto (the real name was Alvise da Ca da Mosto), in 1454. He found at the mouth of the Senegal, trunks of which he estimated the circumference at seventeen fathoms, or 102 feet, (Ramusio, Vol. i. p. 109): he might have compared them with Dragon trees which he had seen before. Perrottet says in his “Flore de Sénégambie” (p. 76), that he had seen monkey bread-trees which, with a height of only about 70 or 80 feet, had a diameter of 32 English feet. The same dimensions had been given by Adanson, in the account of his voyage in 1748; the largest trunks which he himself saw (in 1749) in one of the small Magdalena islands near Cape de Verd, and in the vicinity of the mouth of the Senegal River, were from 26 to 28½ English feet in diameter, with a height of little more than 70 feet, and a top about 180 feet broad; but he adds at the same time, that other travellers had found trunks of nearly 32 English feet diameter. French and Dutch sailors had cut their names on the trees seen by Adanson in letters half a foot long; the dates added to the names shewed these inscriptions to be all of the 16th century, except one which belonged to the 15th. (In Adanson’s “Familles des Plantes,” 1763, P. I. pp. ccxv.-ccxviii., it stands as the 14th century, but this is doubtless an error of inadvertence.) From the depth of the inscriptions, which were covered with new layers of wood, and from the comparison of the thickness of different trunks of the same species in which the relative age of the trees was known, Adanson computed the probable age of the larger trees, and found for a diameter of 32 English feet 5150 years. (Voyage au Sènegal, 1757, p. 66.) He prudently adds (I do not alter his curious orthography):—“Le calcul de l’aje de chake couche n’a pas d’exactitude géometrike.” In the village of Grand Galarques, also in Senegambia, the negroes have ornamented the entrance of a hollow Baobab tree with sculptures cut out of the still fresh wood; the interior serves for holding meetings in which their interests are debated. Such a hall of assembly reminds one of the hollow or cave (specus) of the plane tree in Lycia, in which Lucinius Mutianus, who had previously been consul, feasted with twenty-one guests. Plino (xii. 8) assigns to such a cavity in a hollow tree the somewhat large allowance of a breadth of eighty Roman feet. The Baobab was seen by Réné Caillié in the Valley of the Niger near Jenne, by Caillaud in Nubia, and by Wilhelm Peters along the whole eastern coast of Africa (where it is called Mulapa, i. e. Nlapa-tree, more properly Muti-nlapa) as far as Lourenzo Marques, almost to 26° of S. lat. Although Cadamosto said in the 15th century “eminentia non quadrat magnitudini,” and although Golberry (Fragmens d’un Voyage en Afrique, T. ii. p. 92) found in the “Vallée des deux Gagnacks” trunks which, with 36 English feet diameter near the roots, were only 64 English feet high, yet this great disproportion between height and thickness must not be regarded as general. The learned traveller Peters remarks that “very old trees lose height by the gradual decay of the top, while they continue to increase in girth. On the East Coast of Africa one sees not unfrequently trunks of little more than ten feet diameter reach a height of 69 English feet.”
If, according to what has been said, the bold estimations of Adanson and Perottet assign to the Adansonias measured by them an age of from 5150 to 6000 years, which would make them contemporaneous with the epoch of the building of the Pyramids or even with that of Menes, a period when the constellation of the Southern Cross was still visible in Northern Germany (Kosmos, Bd. iii. S. 402 and 487; Eng. ed. p. 293, and note 146), on the other hand, the more secure estimations made from the annual rings of trees in our northern temperate zone, and from the ratio which has been found to subsist between the thickness of the layer of wood and the time of growth, give us shorter periods. Decandolle finds as the result of his inquiries, that of all European species of trees the yew is that which attains the greatest age. He assigns to the yew (Taxus baccata) of Braborne, in the county of Kent, thirty centuries; to the Scotch yew of Fortingal, from twenty-five to twenty-six; and to those of Crowhurst in Surrey, and Ripon in Yorkshire, respectively, fourteen and a half and twelve centuries. (Decandolle, de la longévité des arbres, p. 65.) Endlicher remarks that the age of another yew tree, in the Churchyard of Grasford, in North Wales, which measures 52 English feet in circumference below the branches, is estimated at 1400 years, and that of a yew in Derbyshire at 2096 years. In Lithuania lime trees have been cut down which were 87 English feet in circumference, and in which 815 annual rings have been counted. (Endlicher, Grundzüge der Botanik, S. 399.) In the temperate zone of the southern hemisphere some species of Eucalyptus attain an enormous girth, and as they also reach to a great stature (above 230 Paris, 245 English, feet), they are singularly contrasted with our yew trees, whose great dimension is in thickness only. Mr. Backhouse found in Emu Bay, on the coast of Van Diemen Land, trunks of Eucalyptus which measured 70 English feet round the trunk near the ground, and five feet higher up 50 English feet. (Gould, Birds of Australia, Vol. I. Introd. p. xv.)
It is not, as is commonly stated, Malpighi, but the ingenious Michel Montaigne, who has the merit of having been the first, in 1581, in his Voyage en Italie, to notice the relation of the annual rings to the age of the tree. (Adrien de Jussieu, Cours élémentaire de Botanique, 1840, p. 61.) A skilful artist, engaged in the preparation of astronomical instruments, had called the attention of Montaigne to the annual rings; and he also maintained that the rings were narrower on the north side of the tree. Jean Jacques Rousseau had the same belief; and his Emile, if he loses himself in a forest, is to direct himself by the indications afforded by the relative thickness of the layers of wood. More recent observations on the anatomy of plants teach us, however, that both the acceleration and also the retardation or intermission of growth, or the varying production of circles of ligneous fascicles (annual deposits) from the Cambium cells, depend on influences which are wholly distinct from the quarter of the heavens towards which one side of the annual rings is turned. (Kunth, Lehrbuch der Botanik, 1847, T. i. S. 146 and 164; Lindley, Introduction to Botany, 2d edition, p. 75.)
Trees which in individual cases attain a diameter of more than twenty feet, and an age extending to many centuries, belong to the most different natural families. I may name here Baobabs, Dragon-trees, some species of Eucalyptus, Taxodium disticum (Rich.), Pinus Lambertiana (Douglas), Hymenæa courbaril, Cæsalpinieæ, Bombax, Swietenia mahagoni, the Banyan tree (Ficus religiosa), Liriodendron tulipifera? Platanus orientalis, and our Limes, Oaks, and Yews. The celebrated Taxodium distichon, the Ahuahuete of the Mexicans, (Cupressus disticha Linn., Schubertia disticha Mirbel); at Santa Maria del Tule, in the state of Oaxaca, has not a diameter of 57, as Decandolle says, but of exactly 38 French (40½ English) feet. (Mühlenpfordt, Versuch einer getreuen Schilderung der Republik Mexico, Bd. i. S. 153.) The two fine Ahuahuetes near Chapoltepec, which I have often seen, and which are probably the surviving remnants of an ancient garden or pleasure-ground of Montezuma, measure, (according to Burkart’s account of his travels, Bd. i. S. 268, a work which otherwise contains much information), only 36 and 38 English feet in circumference; not in diameter, as has often been erroneously asserted. The Buddhists in Ceylon venerate the gigantic trunk of the sacred fig-tree of Anourahdepoura. The Indian fig-tree or Banyan, of which the branches take root round the parent stem, forming, as Onesicritus well described, a leafy canopy resembling a many-pillared tent, often attain a thickness of 28 (29½ English) feet diameter. (Lassen, Indische Alterthumskunde, Bd. i. S. 260.) On the Bombax ceiba, see early notices of the time of Columbus, in Bembo’s Historiæ Venetæ, 1551, fol. 83.
Among oak-trees, of those which have been accurately measured, the largest in Europe is no doubt that near the town of Saintes, in the Departement de la Charente Inférieure, on the road to Cozes. This tree, which is 60 (64 English) feet high, has a diameter of 27 feet 8½ inches (29½ English feet) near the ground; 21½ (almost 23 English) feet five feet higher up; and where the great boughs commence 6 Parisian feet (6 feet 5 inches English.) In the dead part of the trunk a little chamber has been arranged, from 10 feet 8 inches to 12 feet 9 inches wide, and 9 feet 8 inches high (all English measure), with a semi-circular bench cut out of the fresh wood. A window gives light to the interior, so that the sides of the chamber (which is closed with a door) are clothed with ferns and lichens, giving it a pleasing appearance. Judging by the size of a small piece of wood which has been cut out above the door, and in which the marks of 200 annular rings have been counted, the oak of Saintes would be between 1800 and 2000 years old. (Annales de la Société d’Agriculture de la Rochelle, 1843, p. 380.)
In the wild rose-tree of the crypt of the Cathedral of Hildesheim, said to be a thousand years old, it is the root only, and not the stem, which is eight centuries old, according to accurate information derived from ancient and trustworthy original documents, for the knowledge of which I am indebted to the kindness of Stadtgerichts-Assessor Römer. A legend connects the rose-tree with a vow made by the first founder of the cathedral, Ludwig the Pious; and an original document of the 11th century says, “that when Bishop Hezilo rebuilt the cathedral which had been burnt down, he enclosed the roots of the rose-tree with a vault which still exists, raised upon this vault the crypt, which was re-consecrated in 1061, and spread out the branches of the rose-tree upon the walls.” The stem now living is 26½ feet high and about two inches thick, and the outspread branches cover about 32 feet of the external wall of the eastern crypt; it is doubtless of considerable antiquity, and well deserving of the celebrity which it has gained throughout Germany.
If extraordinary development in point of size is to be regarded as a proof of long continued organic life, particular attention is due to one of the thalassophytes of the sub-marine vegetable world, i. e., to the Fucus giganteus, or Macrocystis pyrifera of Agardh. According to Captain Cook and George Forster, this sea-plant attains a length of 360 English feet; surpassing, therefore, the height of the loftiest Coniferæ, even that of the Sequoia gigantea, Endl., or Taxodium sempervirens, Hook and Arnott, which grows in California. (Darwin, Journal of Researches into Natural History, 1845, p. 239; and Captain Fitz-Roy in the Narrative of the Voyages of the Adventure and Beagle, vol. ii. p. 363.) Macrocystis pyrifera is found from 64° south to 45° north latitude, as far as San Francisco on the north-west coast of America; and Joseph Hooker believes it to extend as far as Kamtschatka. In the Antarctic seas it is even seen floating among the pack-ice. (Joseph Hooker, Botany of the Antarctic Voyage under the command of Sir James Ross, 1844, pp. 7, 1, and 178; Camille Montagne, Botanique cryptogame du Voyage de la Bonite, 1846, p. 36.) The immense length to which the bands or ribbands and the cords or lines of the cellular tissue of the Macrocystis attain, appears to be limited only by accidental injuries.
[13] p. 17.—“Species of phænogamous plants already contained in herbariums.”
We must carefully distinguish between three different questions: How many species of plants are described in printed works? how many have been discovered, i. e. are contained in herbariums, though without being described? how many are probably existing on the globe? Murray’s edition of the Linnean system contains, including cryptogamia, only 10042 species. Willdenow, in his edition of the Species Plantarum, between the years 1797 and 1807, had already described 17457 phænogamous species, (from Monandria to Polygamia diœcia.) If we add 3000 cryptogamous species, we obtain the number which Willdenow mentions, viz. 20000 species. More recent researches have shown how much this estimation of the number of species described and contained in herbariums falls short of the truth. Robert Brown counted above 37000 phænogamous plants. (General Remarks on the Botany of Terra Australis, p. 4.) I afterwards attempted to give the geographical distribution (in different parts of the earth already explored), of 44000 phænogamous and cryptogamous plants. (Humboldt, de distributione geographica Plantarum, p. 23.) Decandolle found, in comparing Persoon’s Enchiridium with his Universal System in 12 several families, that the writings of botanists and European herbariums taken together might be assumed to contain upwards of 56000 species of plants. (Essai élementaire de Géographie botanique, p. 62.) If we consider how many species have since that period been described by travellers,—(my expedition alone furnished 3600 of the 5800 collected species of the equinoctial zone),—and if we remember that in all the botanical gardens taken together there are certainly above 25000 phænogamous plants cultivated, we shall easily perceive how much Decandolle’s number falls short of the truth. Completely unacquainted as we still are with the larger portions of the interior of South America,—(Mato-Grosso, Paraguay, the eastern declivity of the Andes, Santa Cruz de la Sierra, and all the countries between the Orinoco, the Rio Negro, the Amazons, and Puruz),—of Africa, Madagascar, Borneo, and Central and Eastern Asia,—the thought rises involuntarily in the mind that we may not yet know the third, or probably even the fifth part of the plants existing on the earth! Drège has collected 7092 species of phænogamous plants in South Africa alone. (See Meyer’s pflanzen geographische Documente, S. 5 and 12.) He believes that the Flora of that district consists of more than 11000 phænogamous species, while on a surface of equal area (12000 German, or 192000 English square geographical miles) von Koch has described in Germany or Switzerland 3300, and Decandolle in France 3645 species of phænogamous plants. I would also recall that even now new Genera, (some even consisting of tall forest trees), are being discovered in the small West Indian Islands which have been visited by Europeans for three centuries, and in the vicinity of large commercial towns. These considerations, which I propose to develop in further detail at the close of the present annotation, make it probable that the actual number of species exceeds that spoken of in the old myth of the Zend-Avesta, which says that “the Primeval Creating Power called forth from the blood of the sacred bull 120000 different forms of plants!”
If, then, we cannot look for any direct scientific solution of the question of how many forms of the vegetable kingdom,—including leafless Cryptogamia (water Algæ, funguses, and lichens), Characeæ, liver-worts, mosses, Marsilaceæ, Lycopodiaceæ, and ferns,—exist on the dry land and in the ocean in the present state of the organic life of our globe, we may yet attempt an approximate method by which we may find some probable “lowest limits” or numerical minima. Since 1815, I have sought, in arithmetical considerations relating to the geography of plants, to examine first the ratios which the number of species in the different natural families bear to the entire mass of the phænogamous vegetation in countries where the latter is sufficiently well known. Robert Brown, the greatest botanist among our cotemporaries, had previously determined the numerical proportions of the leading divisions of the vegetable kingdom; of Acotyledons (Agamæ, Cryptogamic or cellular plants) to Cotyledons (Phanerogamic or vascular plants), and of Monocotyledonous (Endogenous) to Dicotyledonous (Exogenous) plants. He finds the ratio of Monocotyledons to Dicotyledons in the tropical zone as 1 : 5, and in the cold zones of the parallels of 60° N. and 55° S. latitude, as 1 : 2½. (Robert Brown, General Remarks on the Botany of Terra Australis, in Flinders’ Voyage, vol. ii. p. 338.) The absolute number of species in the three leading divisions of the vegetable kingdom are compared together in that work according to the method there laid down. I was the first to pass from these leading divisions to the divisions of the several families, and to consider the ratio which the number of species of each family bears to the entire mass of phænogamous plants belonging to a zone of the earth’s surface. (Compare my memoir entitled De distributione geographica Plantarum secundum cœli temperiem et altitudinem montium, 1817, p. 24-44; and the farther development of the subject of these numerical relations given by me in the Dictionnaire des Sciences naturelles, T. xviii. 1820, p. 422-436; and in the Annales de Chimie et de Physique, T. xvi. 1821, p. 267-292.)
The numerical relations of the forms of plants, and the laws observed in their geographical distribution, may be considered in two very different ways. If plants are studied in their arrangement according to natural families, without regard to their geographical distribution, it is asked, What are the fundamental forms or types of organisation to which the greatest number of species correspond? Are there on the entire surface of the earth more Glumaceæ than Compositæ? Do these two orders make up between them one-fourth part of the whole number of phænogamous plants? What is the proportion of Monocotyledons to Dicotyledons? These are questions of General Phytology, or of the science which investigates the organisation of plants and their mutual connection, or the present state of the entire vegetable world.
If, on the other hand, the species of plants which have been grouped according to the analogy of their structure are considered, not abstractedly, but according to their climatic relations, or according to their distribution over the surface of the earth, we have questions offering quite another and distinct interest. We then examine what are the families which prevail more in proportion to other Phanerogamæ in the torrid zone than towards the polar circle? Are Compositæ more numerous, either in the same geographical latitudes or on the same isothermal lines, in the New than in the Old Continent? Do the forms which gradually lose their predominance in advancing from the equator towards the poles follow a similar law of decrease in ascending mountains situated in the equatorial regions? Do the proportions of particular families to the whole mass of Phanerogamæ differ in the temperate zones, and on equal isothermal lines, north and south of the equator? These questions belong properly to the Geography of Plants, and connect themselves with the most important problems of meteorology and terrestrial physics. The character of a landscape or country is also in a high degree dependent on the predominance of particular families of plants, which render it either desolate or adorned, smiling or majestic. Grasses forming extensive savannahs, Palms and other trees affording food, or social Coniferæ forming forests, have powerfully influenced nations in respect to their material condition, to their manners, to their mental dispositions, and to the more or less rapid development of their prosperity.
In studying the geographical distribution of forms, we may consider species, genera, and natural families, separately. In social plants, a single species often covers extensive tracts of country; as in northern regions forests of Pines or Firs and extensive heaths (ericeta), in Spain cistus-covered grounds, and in tropical America assemblages of the same species of Cactus, Croton, Brathys, or Bambusa Guadua. It is interesting to examine these relations more closely, and to view in one case the great multiplicity of individuals, and in another the variety of organic development. We may inquire what species produces the greatest number of individuals in a particular zone, or we may ask which are the families to which, in different climates, the greatest number of species belong. In a high northern region, where the Compositæ and the Ferns are to the sum of all the phænogamous plants in the ratio of 1 : 13 and 1 : 25 (i. e. where these ratios are found by dividing the sum total of all the Phanerogamæ by the number of species belonging to the family of Compositæ or to that of Filices or Ferns), it may nevertheless happen that a single species of fern covers ten times more ground than do all the species of Compositæ taken together. In this case Ferns predominate over Compositæ by their mass, or by the number of individuals belonging to the same species of Pteris or Polypodium; but they do not so predominate if we only compare the number of the different specific forms of Filices and Compositæ with the sum of all the phænogamous plants. Since, then, multiplication of plants does not follow the same law in all species,—that is to say, all species do not produce the same number of individuals,—therefore the quotients given by dividing the sum of the phænogamous plants by the number of species belonging to one family, do not suffice by themselves to determine the character of the landscape, or the physiognomy which Nature assumes in different regions of the earth. If the attention of the travelling botanist is engaged by the frequent repetition of the same species, their mass, and the uniformity of vegetation thus produced, it is even more arrested by the rarity or infrequency of several other species which are valuable to mankind. In tropical regions, where the Rubiaceæ, Myrtaceæ, Leguminosæ, or Terebinthaceæ, form forests, one is astonished to find the trees of Cinchona, particular species of Swietenia (Mahogany), Hæmatoxylon, Styrax, and balsamic Myroxylum, so sparingly distributed. We had occasion, on the declivities of the high plains of Bogota and Popayan, and in the country round Loxa, in descending towards the unhealthy valley of the Catamayo and to the Amazons River, to remark the manner in which the trees which furnish the precious fever-bark (species of Cinchona) are found singly and at considerable distances from each other. The China Hunters, Cazadores de Cascarilla (the name given at Loxa to the Indians and Mestizoes who collect each year the most efficacious of all fever-barks, that of the Cinchona Condaminea, among the lonely mountains of Caxanuma, Uritusinga, and Rumisitana), climb, not without peril, to the summits of the loftiest forest trees in order to gain a wide prospect, and to discern the solitarily scattered slender aspiring trunks of the trees of which they are in search, and which they recognise by the shining reddish tint of their large leaves. The mean temperature of this important forest region, situated in 4° to 4½° S. lat. and at an elevation of about 6400 to 8000 English feet, is from 12½° to 16° Réaumur (60°·2 to 68° Fahr.) (Humboldt and Bonpland, Plantes équinoxiales, T. i. p. 88, tab. 10.)
In considering the distribution of species, we may also proceed, without regard to the multiplication of individuals, to the masses which they form or the space which they occupy, and may simply compare together the absolute number of species belonging to a particular family in each country. This is the mode of comparison which Decandolle has employed in the work entitled Regni vegetabilis Systema naturale (T. i. p. 128, 396, 439, 464, and 510), and Kunth has carried it out in regard to the whole number of species of Compositæ at present known (above 3300). It does not show which is the predominant family either in the number of species or in the quantity of individuals as compared with other families; it merely tells how many of the species of one and the same family are indigenous in each country or each quarter of the world. The results of this method are on the whole more exact, because they are obtained by the careful study of single families without the necessity of being acquainted with the whole number of the phanerogamæ belonging to each country. The most varied forms of Ferns, for example, are found between the tropics; it is there, in the tempered heat of moist and shaded places in mountainous islands, that each genus presents the largest number of species: this variety of species in each genus diminishes in passing from the tropical to the temperate zone, and decreases still farther in approaching nearer to the pole. Nevertheless, as in the cold zone—in Lapland, for example—those plants succeed best which can best resist the cold, so the species of Ferns, although the absolute number is less than in France or Germany, are yet relatively more numerous than in those countries; i. e. their number bears a greater proportion to the sum total of all the phanerogamous plants of the country. These proportions or ratios, given as above-mentioned by quotients, are in France and Germany 1⁄73 and 1⁄71, and in Lapland 1⁄25. I published numerical ratios of this kind,—(i. e. the entire quantity of phænogamous plants in each of the different Floras divided by the number of species in each family)—in my Prolegomenis de distributione geographica Plantarum, in 1817; and in the Memoir on the distribution of plants over the Earth’s surface, subsequently published in the French language, I corrected my previously published numbers by Robert Brown’s great works. In advancing from the Equator to the Poles, the ratios taken in this manner vary considerably from the numbers which would be obtained from a comparison of the absolute number of species belonging to each family. We often find the value of the fraction increase by the decrease of the denominator, while yet the absolute number of species has diminished. In the method by fractions, which I have followed as more instructive in reference to the geography of plants, there are two variables; for in proceeding from one isothermal line, or one zone of equal temperature, to another, we do not see the sum total of all the phanerogamæ change in the same proportion as does the number of species belonging to a particular family.
We may, if we please, pass from the consideration of species to that of divisions formed in the natural system of botany according to an ideal series of abstractions, and direct our attention to Genera, to Families, and even to the still higher, i. e. more comprehensive, Classes. There are some genera, and even some entire families, which belong exclusively to particular zones of the Earth’s surface; and this not only because they can only flourish under a particular combination of climatic conditions, but also because both the localities in which they originated, and their migrations, have been limited. It is otherwise with the greater number of genera and of families, which have their representatives in all regions of the globe, and at all latitudes of elevation. The earliest investigations into the distribution of vegetable forms related solely to genera; we find them in a valuable work of Treviranus, in his Biology (Bd. ii. S. 47, 63, 83, and 129). This method is, however, less fitted to afford general results than that which compares either the number of species of each family, or the great leading divisions (of Acotyledons, Monocotyledons, and Dicotyledons) with the sum of all the phanerogamæ. We find that in the cold zones the variety of forms does not decrease so much if estimated by genera as if estimated by species; in other words, we find relatively more genera and fewer species. (Decandolle, Théorie élémentaire de la Botanique, p. 190; Humboldt, Nova genera et species Plantarum, T. i pp. xvi. and 1.) It is almost the same in the case of high mountains whose summits support single members of a large number of genera, which we should have been à priori inclined to regard as belonging exclusively to the vegetation of the plains.
I have thought it desirable to indicate the different points of view from which the laws of the geographical distribution of plants may be considered. It is by confounding these different points of view that apparent contradictions are found; which are unjustly attributed to uncertainties of observation. (Jahrbücher der Gewächskunde, Bd. i Berlin, 1818, S. 18, 21, 30.) When such expressions as the following are made use of—“This form, or this family, diminishes as the cold zones are approached;—it has its true home in such or such a latitude;—it is a southern form;—it predominates in the temperate zone;” care should always be taken to state expressly whether the writer is speaking of the absolute number of species, and its increase or decrease with the change of latitude; or whether he means that the family in question prevails over other families of plants as compared with the entire number of phanerogamæ of which a Flora consists. The impression of prevalence as conveyed by the eye depends on relative quantity.
Terrestrial physics have their numerical elements, as has the System of the Universe, or Celestial Physics, and by the united labours of botanical travellers we may expect to arrive gradually at a true knowledge of the laws which determine the geographical and climatic distribution of vegetable forms. I have already remarked that in the temperate zone the Compositæ (Synanthereæ), and the Glumaceæ (including under this latter name the three families of Grasses, Cyperoidæ and Juncaceæ), make up the fourth part of all phænogamous plants. The following numerical ratios are the results of my investigations for 7 great families of the vegetable kingdom in the same temperate zone.
Glumaceæ 1⁄8 (Grasses alone 1⁄12)
Compositæ 1⁄8
Leguminosæ 1⁄18
Labiatæ 1⁄24
Umbelliferæ 1⁄40
Amentaceæ (Cupuliferæ, Betulineæ, and Salicineæ) 1⁄45
Cruciferæ 1⁄19
The forms of organic beings are in reciprocal dependence on each other. In the unity of nature these forms limit each other according to laws which are probably attached to periods of long duration. If on any particular part of the globe we know with accuracy the number of species of one of the great families of Glumaceæ, Leguminosæ, or Compositæ, we may with a tolerable degree of probability form approximative inferences, both as to the sum of all the phanerogamæ of the country, and also as to the number of species belonging to the rest of the leading families of plants. The number of Cyperoidæ determines that of Compositæ, and the number of Compositæ that of Leguminosæ; they even enable us to judge in what classes or orders the Floras of countries are still incomplete, and teach us, if we are on our guard against confounding together very different systems of vegetation, what harvest may still remain to be reaped in the several families.
The comparison of the numerical ratios of families in different already well explored zones, has conducted me to the recognition of laws according to which, in proceeding from the equator to the poles, the vegetable forms constituting a natural family decrease or increase as compared with the whole mass of phanerogamæ belonging to each zone. We have here to regard not only the direction of the change (whether an increase or a decrease), but also its rapidity or measure. We see the denominator of the fraction which expresses the ratio increase or decrease: let us take as our example the beautiful family of Leguminosæ, which decreases in going from the equinoctial zone towards the North Pole. If we find its proportion or ratio for the torrid zone (from 0° to 10° of latitude) at 1⁄10, we obtain for the part of the temperate zone which is between 45° and 52° latitude 1⁄18, and for the frigid zone (lat. 67° to 70°) only 1⁄35. The direction followed by the great family of Leguminosæ (increase on approaching the equator), is also that of the Rubiaceæ, the Euphorbiaceæ, and especially the Malvaceæ. On the contrary, the Grasses and Juncaceæ (the latter still more than the former), diminish in approaching the equator, as do also the Ericeæ and Amentaceæ. The Compositæ, Labiatæ, Umbelliferæ, and Cruciferæ, decrease in proceeding from the temperate zone, either towards the pole or towards the equator, the Umbelliferæ and Cruciferæ decreasing most rapidly in the last-named direction; while at the same time in the temperate zone the Cruciferæ are three times more numerous in Europe than in the United States of North America. On reaching Greenland the Labiatæ have entirely disappeared with the exception of one, and the Umbelliferæ with the exception of two species; the entire number of phænogamous species, still amounting, according to Hornemann, to 315 species.
It must be remarked at the same time that the development of plants of different families, and the distribution of vegetable forms, does not depend exclusively on geographical, or even on isothermal latitude; the quotients are not always on the same isothermal line in the temperate zone, for example, in the plains of North America and those of the Old Continent. Within the tropics there is a very sensible difference between America, India, and the West Coast of Africa. The distribution of organic beings over the surface of the earth does not depend wholly on thermic or climatic relations, which are of themselves very complicated, but also on geological causes almost unknown to us, belonging to the original state of the earth, and to catastrophes which have not affected all parts of our planet simultaneously. The large pachydermatous animals are at the present time wanting in the New Continent, while we still find them in analogous climates in Asia and Africa. These differences ought not to deter us from endeavouring to search out the concealed laws of nature, but should rather stimulate us to the study of them through all their intricacies.
The numerical laws of the families of plants, the often striking agreement of the numbers expressing their ratios, where yet the species of which the families consist are for the most part different, conduct us into the mysterious obscurity which envelopes all that is connected with the fixing of organic types in the species of plants and animals, or with their original formation or creation. I will take as examples two adjoining countries which have both been thoroughly explored—France and Germany. In France, many species of Grasses, Umbelliferæ and Cruciferæ, Compositæ, Leguminosæ, and Labiatæ, are wanting which are common in Germany; and yet the numerical ratios of these six great families are almost identical in the two countries, as will be seen by the subjoined comparison.
| Families. | Germany. | France. |
|---|---|---|
| Gramineæ. | 1⁄13 | 1⁄13 |
| Umbelliferæ. | 1⁄22 | 1⁄21 |
| Cruciferæ. | 1⁄18 | 1⁄19 |
| Compositæ. | 1⁄8 | 1⁄7 |
| Leguminosæ. | 1⁄18 | 1⁄16 |
| Labiatæ. | 1⁄26 | 1⁄24 |
This agreement in the number of species in each family compared to the whole number of phenogamous species in the Floras of France and Germany, would not by any means exist if the German species which are missing in France were not replaced there by other types belonging to the same families. Those who are fond of imagining gradual transformations of species, and suppose the different kinds of parrots proper to two islands not far removed from each other to present examples of such a change, will be inclined to attribute the remarkable similarity between the two columns of figures which have just been given, to a migration of species, which, having been the same at first, have been altered gradually by the long-continued action of climatic causes during thousands of years, so that their identity being lost they appear to replace each other. But why is it that our common heather (Calluna vulgaris), why is it that our oaks have never advanced to the eastward of the Ural Mountains, and so passed from Europe to Northern Asia? Why is there no species of the genus Rosa in the Southern Hemisphere, and why are there scarcely any Calceolarias in the Northern Hemisphere? The necessary conditions of temperature are insufficient to explain this. Thermic relations alone cannot, any more than the hypothesis of migrations of plants radiating from certain central points, explain the present distribution of fixed organic forms. Thermic relations are hardly sufficient to explain the limits beyond which individual species do not pass, either in latitude towards the pole at the level of the sea, or in vertical elevation towards the summits of mountains. The cycle of vegetation in each species, however different its duration may be, requires, in order to be successfully passed through, a certain minimum of temperature. (Playfair, in the Transactions of the Royal Society of Edinburgh, vol. v. 1805, p. 202; Humboldt, on the sum of the degrees of temperature required for the cycle of vegetation in the Cerealia, in Mem. sur les lignes isothermes, p. 96; Boussingault, Economie rurale, T, ii. p. 659, 663, and 667; Alphonse Decandolle sur les causes qui limitent les espèces végétales, 1847, p. 8.) But all the conditions necessary for the existence of a plant, either as diffused naturally or by cultivation,—conditions of latitude or minimum distance from the pole, and of elevation or maximum height above the level of the sea,—are farther complicated by the difficulty of determining the commencement of the thermic cycle of vegetation, and by the influence which the unequal distribution of the same quantity of heat into groups of successive days and nights exercises on the excitability, the progressive development, and the whole vital process; to all this must be farther added hygrometric influences and those of atmospheric electricity.
My investigations respecting the numerical laws of the distribution of forms may possibly be applied at some future day with advantage to the different classes of Rotiferæ in the animal creation. The rich collections at the Museum d’Histoire Naturelle in the Jardin des Plantes at Paris, already contained, in 1820, (according to approximate estimations) above 56000 phænogamous and cryptogamous plants in herbariums, 44000 insects (a number doubtless too small, though given me by Latreille), 2500 species of fish, 700 reptiles, 4000 birds, and 500 mammalia. Europe has about 80 species of indigenous mammalia, 400 birds, and 30 reptiles. In the Northern temperate zone, therefore, the species of birds are five times more numerous than those of mammalia, as there are in Europe five times as many Compositæ as there are Amentaceæ and Coniferæ, and five times as many Leguminosæ as there are Orchideæ and Euphorbiaceæ. In the southern hemisphere the ratio of mammalia is in tolerably striking agreement, being as 1 to 4·3. Birds, and still more reptiles, increase in the number of species in approaching the torrid zone more than the mammalia. Cuvier’s researches might lead us to believe that the proportion was different in the earlier state of things, and that many more mammalia had perished by revolutions of Nature than birds. Latreille has shewn what groups of insects increase towards the pole, and what towards the equator. Illiger has given the countries of 3800 species of birds according to the quarters of the globe: it would have been much more instructive if the same thing had been done according to zones. We should find little difficulty in comprehending how on a given space of the earth’s surface the individuals of a class of plants or animals limit each other’s numbers, or how, after long continued contest and many fluctuations caused by the requirements of nourishment and mode of life, a state of equilibrium should be at last established; but the causes which have limited not the number of individuals of a form, but the forms themselves, in a particular space, and founded their typical diversity, are placed beneath the impenetrable veil which still conceals from our eyes all that relates to the manner of the first creation and commencement of organic beings.
If, then, we would attempt to solve the question spoken of in the early part of this dissertation, by giving in an approximate manner the numerical limit, (le nombre limite of French mathematicians), which the whole phanerogamæ now existing on the surface of the earth cannot be supposed to fall short of, we may perhaps find our safest guide in a comparison of the numerical ratios (which, as we have seen, may be assumed to exist between the different families of plants), with the number of species contained in herbariums and cultivated in our great botanic gardens. I have said that in 1820 the number of species contained in the herbariums of the Jardin des Plantes at Paris was already estimated at 56000. I do not permit myself to conjecture the amount which the herbariums of England may contain; but the great Paris herbarium, which was formed with much personal sacrifice by Benjamin Delessert, and given by him for free and general use, was stated at his death to contain 86000 species; a number almost equal to that which, as late as 1835, was conjecturally assigned by Lindley as that of all the species existing on the whole earth. (Lindley, Introduction to Botany, 2d edit. p. 504.) Few herbariums have been reckoned with care, after a complete and strict separation and withdrawal of all mere varieties. Not a few plants contained in smaller collections are still wanting in the greater herbariums which are supposed to be general or complete. Dr. Klotzsch estimates the present entire number of phænogamous plants in the great Royal Herbarium at Schöneberg, near Berlin, of which he is the curator, at 74000 species.
Loudon’s useful work, Hortus Britannicus, gives an approximate view of all the species which are, or at no remote time have been, cultivated in British gardens: the edition of 1832 enumerates, including indigenous plants, exactly 26660 phænogamous species. We must not confound with this large number of plants which have grown or been cultivated at any time and in any part of the whole British Islands, the number of living plants which can be shewn at any single moment of time in any single botanic garden. In this last-named respect the Botanic Garden of Berlin has long been regarded as one of the richest in Europe. The fame of its extraordinary riches rested formerly only on uncertain and approximate estimations, and, as my fellow-labourer and friend of many years’ standing, Professor Kunth, has justly remarked (in manuscript notices communicated to the Gartenbau-Verein in December 1846), “no real enumeration or computation could be made until a systematic catalogue, based on a rigorous examination of species, had been prepared. Such an enumeration has given rather above 14060 species: if we deduct from this number 375 cultivated Ferns, we have remaining 13685 phænogamous species; among which we find 1600 Compositæ, 1150 Leguminosæ, 428 Labiatæ, 370 Umbelliferæ, 460 Orchideæ, 60 Palms, and 600 Grasses and Cyperaceæ. If we compare with these numbers those of the species already described in recent works,—Compositæ (Decandolle and Walpers) about 10000; Leguminosæ, 8070; Labiatæ (Bentham), 2190; Umbelliferæ, 1620; Grasses, 3544; and Cyperaceæ (Kunth, Enumeratio Plantarum), 2000;—we shall perceive that the Berlin Botanic Garden cultivates, of the very large families (Compositæ, Leguminosæ, and Grasses), only 1-7th, 1-8th, and 1-9th;—and of the small families (Labiatæ and Umbelliferæ), about 1-5th, or 1-4th, of described species. If, then, we estimate the number of all the different phænogamous plants cultivated at one time in all the botanic gardens of Europe at 20000, we find that the cultivated species appear to be about the eighth part of those which are already either described or preserved in herbariums, and that these must nearly amount to 160000. This estimate need not be thought excessive, since of many of the larger families, (for example, Guttiferæ, Malpighiaceæ, Melastomeæ, Myrtaceæ, and Rubiaceæ), hardly a hundredth part are found in our garden.” If we take the number given by Loudon in his Hortus Britannicus (26660 species) as a basis, we shall find, (according to the justly drawn succession of inferences of Professor Kunth, in the manuscript notices from which I have borrowed the above), the estimate of 160000 species rise to 213000; and even this is still very moderate, for Heynhold’s Nomenclator botanicus hortensis (1846) even rates the phænogamous species then cultivated at 35600; whereas I have employed Loudon’s number for 1832, viz. 26660. On the whole it would appear from what has been said,—and the conclusion is at first sight a sufficiently striking one,—that at present there are almost more known species of phænogamous plants (with which we are acquainted by gardens, descriptions, or herbariums), than there are known insects. According to the average of the statements which I have received from several of our most distinguished entomologists whom I have had the opportunity of consulting, the number of insects at present described, or contained in collections without being described, may be taken at between 150000 and 170000 species. The rich Berlin collection does not contain less than 90000 species, among which are about 82000 Coleoptera. A very large number of plants have been collected in distant parts of the globe, without the insects which live on them or near them being brought at the same time. If, however, we limit the estimates of numbers to a single part of the world, and that the one which has been the best explored in respect to both plants and insects, viz. Europe, we find a very different proportion; for while we can hardly enumerate between seven and eight thousand European phænogamous plants, more than three times that number of European insects are already known. According to the interesting communications of my friend Dohrn at Stettin, 8700 insects have already been collected from the rich Fauna of that vicinity, (and many micro-Lepidopteræ are still wanting), while the phænogamous plants of the same district scarcely exceed 1000. The Insect Fauna of Great Britain is estimated at 11600 species. Such a preponderance of animal forms need the less surprise us, since large classes of insects subsist solely on animal substances, and others on agamous vegetation (funguses, and even those which are subterranean). Bombyx pini alone (the spider which infests the Scotch fir, and is the most destructive of all forest insects), is visited, according to Ratzeburg, by thirty-five parasitical Ichneumonides.
If these considerations have led us to the proportion borne by the species of plants cultivated in gardens to the entire amount of those which are already either described or preserved in herbariums, we have still to consider the proportion borne by the latter to what we conjecture to be the whole number of forms existing upon the earth at the present time; i. e. to test the assumed minimum of such forms by the relative numbers of species in the different families, therefore, by uncertain multipliers. Such a test, however, gives for the lowest limit or minimum number results so low as to lead us to perceive that even in the great families,—our knowledge of which has been of late most strikingly enriched by the descriptions of botanists,—we are still acquainted with only a small part of existing plants. The Repertorium of Walpers completes Decandolle’s Prodromus of 1825, up to 1846: we find in it, in the family of Leguminosæ, 8068 species. We may assume the ratio, or relative numerical proportion of this family to all phænogamous plants, to be 1⁄21—as we find it 1⁄10 within the tropics, 1⁄18 in the middle temperate, and 1⁄33 in the cold northern zone. The described Leguminosæ would thus lead us to assume only 169400 existing phænogamous species on the whole surface of the earth, whereas, as we have shewn, the Compositæ indicate more than 160000 already known species. The discordance is instructive, and may be further elucidated and illustrated by the following analogous considerations.
The major part of the Compositæ, of which Linnæus knew only 785 species and which has now grown to 12000, appear to belong to the Old Continent: at least Decandolle described only 3590 American, whilst the European, Asiatic, and African species amounted to 5093. This apparent richness in Compositæ is, however, illusive, and considerable only in appearance; the ratio or quotient of the family, (1⁄15 between the tropics, 1⁄7 in the temperate zone, and 1⁄13 in the cold zone), shews that even more species of Compositæ than Leguminosæ must hitherto have escaped the researches of travellers; for a multiplication by 12 would give us only the improbably low number of 144000 Phænogamous species. The families of Grasses and Cyperaceæ give still lower results, because comparatively still fewer of their species have been described and collected. We have only to cast our eyes on the map of South America, remembering the wide extent of territory occupied by grassy plains, not only in Venezuela and on the banks of the Apure and the Meta, but also to the south of the forest-covered regions of the Amazons, in Chaco, Eastern Tucuman, and the Pampas of Buenos Ayres and Patagonia, bearing in mind that of all these extensive regions the greater part have never been explored by botanists, and the remainder only imperfectly and incompletely so. Northern and Central Asia offer an almost equal extent of Steppes, but in which, however, dicotyledonous herbaceous plants are more largely mingled with the Gramineæ. If we had sufficient grounds for believing that we are now acquainted with half the phænogamous plants on the globe, and if we took the number of known species only at one or other of the before-mentioned numbers of 160000 or 213000, we should still have to take the number of grasses (the general proportion of which appears to be 1⁄12), in the first case at least at 26000, and in the second case at 35000 different species, which would give respectively in the two cases only either 1⁄8 or 1⁄10 part as known.
The assumption that we already know half the existing species of phænogamous plants is farther opposed by the following considerations. Several thousand species of Monocotyledons and Dycotyledons, and among them tall trees,—(I refer here to my own Expedition),—have been discovered in regions, considerable portions of which had been previously examined by distinguished botanists. The portions of the great continents which have never even been trodden by botanical observers considerably exceed in area those which have been traversed by such travellers, even in a superficial manner. The greatest variety of phænogamous vegetation, i. e. the greatest number of species on a given area, is found between the tropics, and in the sub-tropical zones. This last-mentioned consideration renders it so much the more important to remember how almost entirely unacquainted we are, on the New Continent, north of the equator, with the Floras of Oaxaca, Yucatan, Guatimala, Nicaragua, the Isthmus of Panama, Choco, Antioquia, and the Provincia de los Pastos;—and south of the equator, with the Floras of the vast forest region: between the Ucayale, the Rio de la Madera, and the Tocantin (three great tributaries of the Amazons), and with those of Paraguay and the Provincia de los Missiones. In Africa, except in respect to the coasts, we know nothing of the vegetation from 15° north to 20° south latitude; in Asia we are unacquainted with the Floras of the south and south-east of Arabia, where the highlands rise to about 6400 English feet above the level of the sea,—of the countries between the Thian-schan, the Kuenlün, and the Himalaya, all the west part of China, and the greater part of the countries beyond the Ganges. Still more unknown to the botanist are the interior of Borneo, New Guinea, and part of Australia. Farther to the south the number of species undergoes a wonderful diminution, as Joseph Hooker has well and ably shewn from his own observation in his Antarctic Flora. The three islands of which New Zealand consists extend from 34½° to 47¼° S. latitude, and as they contain, moreover, snowy mountains of above 8850 English feet elevation, they must include considerable diversity of climate. The Northern Island has been examined with tolerable completeness from the voyage of Banks and Solander to Lesson and the Brothers Cunningham and Colenso, and yet in more than 70 years we have only become acquainted with less than 700 phænogamous species. (Dieffenbach, Travels in New Zealand, 1843, vol. i. p. 419.) The paucity of vegetable corresponds to the paucity of animal species. Joseph Hooker, in his Flora Antarctica, p. 73-75, remarks that the “botany of the densely wooded regions of the Southern Islands of the New Zealand groups and of Fuegia is much more meagre not only than that of similarly clothed regions of Europe, but of islands many degrees nearer to the Northern pole than these are to the Southern one. Iceland, for instance, which is from 8 to 10 degrees farther from the equator than the Auckland and the Campbell Islands, contains certainly five times as many flowering plants. In the Antarctic Flora, under the influence of a cool and moist, but singularly equable climate, great uniformity, arising from paucity of species, is associated with great luxuriance of vegetation. This striking uniformity prevails both at different levels, (the species found on the plains appearing also on the slopes of the mountains), and over vast extents of country, from the south of Chili to Patagonia, and even to Tierra del Fuego, or from lat. 45° to 56°. Compare, on the other hand, in the northern temperate region, the Flora of the South of France, in the latitude of the Chonos Archipelago on the coast of Chili, with the Flora of Argyleshire in Scotland in the latitude of Cape Horn, and how great a difference of species is found; while in the Southern Hemisphere the same types of vegetation pass through many degrees of latitude. Lastly, on Walden Island, in lat. 80½° N., or not ten degrees from the North Pole of the earth, ten species of flowering plants have been collected, while in the southernmost islet of the South Shetlands, though only in lat. 63° S., only a solitary grass was found.” These considerations on the distribution of plants confirm the belief that the great mass of still unobserved, uncollected, and undescribed flowering plants must be sought for in tropical countries, and in the latitudes from 12° to 15° distant from the tropics.
It has appeared to me not unimportant to show the imperfect state of our knowledge in this still little cultivated department of arithmetical botany, and to propound numerical questions in a more distinct and determinate manner than could have been previously done. In all conjectures respecting numerical relations we must seek first for the possibility of deducing the lower or minimum limits; as in a question treated of by me elsewhere, on the proportion of coined gold and silver to the quantity of the precious metal fabricated in other ways; or as in the questions of how many stars, from the 10th to the 12th magnitude, are dispersed over the sky, and how many of the smallest telescopic stars the Milky Way may contain. (John Herschel, Results of Astron. Observ. at the Cape of Good Hope, 1847, p. 381.) We may consider it as established, that if it were possible to know completely and thoroughly by observation all the species belonging to one of the great families of phanerogamous or flowering plants, we should learn thereby at the same time, approximatively, the entire sum of all such plants (including all the families). As, therefore, by the progressive exploration of new countries we progressively and gradually exhaust the remaining unknown species of any of the great families, the previously assigned lowest limit rises gradually higher, and since the forms reciprocally limit each other in conformity with still undiscovered laws of universal organisation, we approach continually nearer to the solution of the great numerical problem of organic life. But is the number of organic forms itself a constant number? Do new vegetable forms spring from the ground after long periods of time, while others become more and more rare, and at last disappear? Geology, by means of her historical monuments of ancient terrestrial life, answers to the latter portion of this question affirmatively. “In the Ancient World,” to use the remark of an eminent naturalist, Link (Abhandl. der Akad. der Wiss. zu Berlin aus dem Jahr 1846, S. 322), “we see characters, now apparently remote and widely separated from each other, associated or crowded together in wondrous forms, as if a greater development and separation awaited a later age in the history of our planet.”