The same notion of general resemblance and affinity, accompanied with the same vagueness, is to be found in the writer who least participated in the general admiration of Linnæus, Buffon. Though it was in a great measure his love of higher views which made him dislike what he considered the pedantry of the Swedish school, he does not seem to have obtained a clearer sight of the principle of the natural method than his rival, except that he did not restrict his Characters to the fructification. Things must be arranged by their resemblances and differences, (he says in 175026,) ‘but the resemblances and differences must be taken not from one part but from the whole; and we must attend to the form, the size, the habit, the number and position of the parts, even the substance 128 of the part; and we must make use of these elements in greater or smaller number, as we have need.’
14. Method of General Comparison.—A countryman of Buffon, who shared with him his depreciating estimate of the Linnæan system, and his wish to found a natural system upon a broader basis, was Adanson; and he invented an ingenious method of apparently avoiding the vagueness of the practice of following the general feeling of resemblance. This method consisted in making many Artificial Systems, in each of which plants were arranged by some one part; and then collecting those plants which came near each other in the greatest number of those Artificial Systems, as plants naturally the most related. Adanson gives an account27 of the manner in which this system arose in his mind. He had gone to Senegal, animated by an intense zeal for natural history; and there, amid the luxuriant vegetation of the torrid zone, he found that the methods of Linnæus and Tournefort failed him altogether as means of arranging his new botanical treasures. He was driven to seek a new system. ‘For this purpose,’ he says, ‘I examined plants in all their parts, without omitting any, from the roots to the embryo, the folding of the leaves in the bud, their mode of sheathing28, the situation and folding of the embryo and of its radicle in the seed, relatively to the fruit; in short, a number of particulars which few botanists notice. I made in the first place a complete description of each plant, putting each of its parts in separate articles, in all its details; when new species occurred I put down the points in which they differed, omitting those in which they agreed. By means of the aggregate of these comparative descriptions, I perceived that plants arranged themselves into classes or families which could not be artificial or arbitrary, not being founded upon one or two parts, which might change at certain limits, but on all the parts; so that the disproportion of one of these parts was corrected and balanced by the introduction of another.’ Thus the principle of Resemblance 129 was to suffice for the general arrangement, not by means of a new principle, as Symmetry or Organization, which should regulate its application, but by a numeration of the peculiarities in which the resemblance consisted.
The labour which Adanson underwent in the execution of this thought was immense. By taking each Organ, and considering its situation, figure, number, &c., he framed sixty-five Artificial Systems; and collected his Natural Families by a numerical combination of these. For example, his sixty-fifth Artificial System29 is that which depends upon the situation of the Ovary with regard to the Flower; according to this system he frames ten Artificial Classes, including ninety-three Sections: and of these Sections the resulting Natural Arrangement retains thirty-five, above one-third: the same estimate is applied in other cases.
But this attempt to make Number supply the defects which the vague notion of Resemblance introduces, however ingenious, must end in failure. For, as Decandolle observes30, it supposes that we know, not only all the Organs of plants, but all the points of view in which it is possible to consider them; and even if this assumption were true, which it is not, and must long be very far from being, the principle is altogether vicious; for it supposes that all these points of view, and all the resulting artificial systems are of equal importance:—a supposition manifestly erroneous. We are thus led back to the consideration of the Relative Importance of Organs and their qualities, as a basis for the classification of plants, which no Artificial Method can supersede; and thus we find the necessity of attending to something besides mere external and detached Resemblance. The method of General Comparison cannot, any more than the method of Blind Trial, lead us, with any certainty or clearness, to the Natural Method. Adanson’s Families are held by the best botanists to be, for the greater part, Natural; but his hypotheses are unfounded; and his success is 130 probably more due to the dim feeling of Affinity, by which he was unconsciously guided, than to the help he derived from his numerical processes.
In a succeeding chapter I shall treat of that Natural Affinity on which a Natural System must really be founded. But before proceeding to this higher subject, we must say a few words on some of the other parts of the philosophy of Natural History,—the Gradation of Groups, the Nomenclature, the Diagnosis, and the application of the methods to other subjects.
Sect. V.—Gradation of Groups.
15. It has been already noticed (last chapter,) that even that vague application of the idea of resemblance which gives rise to the terms of common language, introduces a subordination of classes, as man, animal, body, substance. Such a subordination appears in a more precise form when we employ this idea in a scientific manner as we do in Natural History. We have then a series of divisions, each inclusive of the lower ones, which are expressed by various metaphors in different writers. Thus some have gone as far as eight terms of the series31, and have taken, for the most part, military names for them; as Hosts, Legions, Phalanxes, Centuries, Cohorts, Sections, Genera, Species. But the most received series is Classes, Orders, Genera, and Species; in which, however, we often have other terms interpolated, as Sub-genera, or Sections of genera. The expressions Family and Tribe, are commonly appropriated to natural groups; and we speak of the Vegetable, Animal, Mineral Kingdom; but the other metaphors of Provinces, Districts, &c., which this suggests, have not been commonly used32.
It will of course be understood that each ascending step of classification is deduced by the same process from the one below. A Genus is a collection of Species which resemble each other more than they 131 resemble other species; an Order is a collection of Genera having, in like manner, the first degree of resemblance, and so on. How close or how wide the Degrees of Resemblance are, must depend upon the nature of the objects compared, and cannot possibly be prescribed beforehand. Hence the same term, Class and Order for instance, may imply, in different provinces of nature, very different degrees of resemblance. The Classes of Animals are Insects, Birds, Fish, Beasts, &c. The Orders of Beasts are Ruminants, Tardigrades, Plantigrades, &c. The two Classes of Plants (according to the Natural Order33) are Vascular and Cellular, the latter having neither sexes, flowers, nor spiral vessels. The Vascular Plants are divided into Orders, as Umbelliferæ, Ranunculaceæ, &c.; but between this Class and its Orders are interposed two other steps:—two Sub-classes, Dicotyledonous and Monocotyledonous, and two Tribes of each: Angiospermiæ, Gymnospermiæ of the first; and Petaloideæ, Glumaciæ of the second. Such interpolations are modifications of the general formula of subordination, for the purpose of accommodating it to the most prominent natural affinities.
16. Species.—As we have already seen in tracing the principles of the Natural Method, when by the intimate study of plants we seek to give fixity and definiteness to the notion of resemblance and affinity on which all these divisions depend, we are led to the study of Organization and Analogy. But we make a reference to physiological conditions even from the first, with regard to the lowest step of our arrangement, the Species; for we consider it a proof of the impropriety of separating two Species, if it be shown that they can by any course of propagation, culture, and treatment, the one pass into the other. It is in this way, for example, that it has been supposed to be established that the common Primrose, Oxlip, Polyanthus, and Cowslip, are all the same species. Plants which thus, in virtue of external circumstances, as soil, 132 exposure, climate, exhibit differences which may disappear by changing the circumstances, are called Varieties of the species. And thus we cannot say that a Species is a collection of individuals which possess the First Degree of Resemblance; for it is clear that a primrose resembles another primrose more than it does a cowslip; but this resemblance only constitutes a Variety. And we find that we must necessarily include in our conception of Species, the notion of propagation from the same stock. And thus a Species has been well defined34: ‘The collection of the individuals descended from one another, or from common parents, and of those which resemble these as much as these resemble each other.’ And thus the sexual doctrine of plants, or rather the consideration of them as things which propagate their kind, (whether by seed, shoot, or in any other way,) is at the basis of our classifications.
17. The First permanent Degree of Resemblance among organized beings is thus that which depends on this relation of generation, and we might expect that the groups which are connected by this relation would derive their names from the notion of generation. It is curious that both in Greek and Latin languages and in our own, the words which have this origin (γένος, genus, kind,) do not, in the phraseology of science at least, denote the nearest degree of relationship, but have other terms subordinate to them, which appear etymologically to indicate a mere resemblance of appearance (εἶδος, species, sort); and these latter terms are appropriated to the groups resulting from propagation. Probably the reason of this is, that the former terms (genus, &c.) had been applied so widely and loosely before the scientific fixation of terms, that to confine them to what we call species would have been to restrict them in a manner too unusual to be convenient.
18. Varieties. Races.—The Species, as we have said, is the collection of individuals which resemble each other as much as do the offspring of a common 133 stock. But within the limits of this boundary, there are often observable differences permanent enough to attract our notice, though capable of being obliterated by mixture in the course of generation. Such different groups are called Varieties. Thus the Primrose and Cowslip, as has been stated above, are found to be varieties of the same plant; the Poodle and the Greyhound are well marked varieties of the species dog. Such differences are hereditary, and it may be long doubtful whether such hereditary differences are varieties only, or different species. In such cases the term Race has been applied.
Sect. VI.—Nomenclature.
19. The Nomenclature of any branch of Natural History is the collection of names of all its species; which, when they become extremely numerous, requires some artifice to make it possible to recollect or apply them. The known species of plants, for example, were 10,000 at the time of Linnæus, and are now probably 60,000. It would be useless to endeavour to frame and employ separate names for each of these species.
The division of the objects into a subordinated system of classification enables us to introduce a Nomenclature which does not require this enormous number of names. The artifice employed to avoid this inconvenience is to name a Species by means of two (or it might be more) steps of the successive division. Thus in Botany, each of the genera has its name, and the species are marked by the addition of some epithet to the name of the genus. In this manner about 1,700 generic names, with a moderate number of specific names, were found by Linnæus sufficient to designate with precision all the species of vegetables known at his time. And this Binary Method of Nomenclature has been found so convenient that it has been universally adopted in every other department of the Natural History of organized beings.
Many other modes of Nomenclature have been tried, but no other has at all taken root. Linnæus himself 134 appears at first to have intended marking each species by the Generic Name accompanied by a characteristic Descriptive Phrase; and to have proposed the employment of a trivial Specific Name, as he termed it, only as a method of occasional convenience. The use of these trivial names, has, however, become universal, as we have said, and is by many persons considered the greatest improvement introduced at the Linnæan reform.
Both Linnæus and other writers (as Adanson) have given many maxims with a view of regulating the selection of generic and specific names. The maxims of Linnæus were intended as much as possible to exclude barbarism and confusion, and have, upon the whole, been generally adopted; though many of them were objected to by his contemporaries (Adanson and others35), as capricious or unnecessary innovations. Many of the names, introduced by Linnæus, certainly appear fanciful enough: thus he gives the name of Bauhinia to a plant with leaves in pairs, because the Bauhins were a pair of brothers; Banisteria is the name of a climbing plant, in honour of Banister, who travelled among mountains. But such names, once established by adequate authority, lose all their inconvenience, and easily become permanent; and hence the reasonableness of the Linnæan rule36, that as such a perpetuation of the names of persons by the names of plants is the only honour botanists have to bestow, it ought to be used with care and caution.
The generic name must, as Linnæus says, be fixed37 before we attempt to form a specific name; ‘the latter without the former is like the clapper without the bell.’ The name of the genus being established, the species may be marked by adding to it ‘a single word taken at will from any quarter;’ that is, not involving a description or any essential property of the plant, but a casual or arbitrary appellation38. Thus the 135 various species of Hieracium39 are Hieracium Alpinum, H. Halleri, H. Pilosella, H. dubium, H. murorum, &c. where we see how different may be the kind of origin of the words.
Attempts have been made at various times to form the name of species from those of genera in some more symmetrical manner. Thus some have numbered the species of genus, 1, 2, 3, &c.; but this method is liable to the inconveniences, first, that it offers nothing for the memory to take hold of; and second, that if a new species intermediate between 1 and 2, 2 and 3, &c., be discovered, it cannot be put in its place. It has also been proposed to mark the species by altering the termination of the genus. Thus Adanson40, denoting a genus by the name Fonna (Lychnidea), conceived he might mark five of its species by altering the last vowel, Fonna, Fonna-e, Fonna-i, Fonna-o, Fonna-u; then others by Fonna-ha, Fonna-ka, and so on. This course would be liable to the same evils which have been noticed as belonging to the numerical method.
The names of plants (and the same is true of animals) have in common practice been binary only, consisting of a generic and a specific name. The Class and Order have not been admitted to form part of the appellation of the species. Indeed it is easy to see that a name which must be identical in so many instances as that of an Order would be, would be felt as superfluous and burdensome. Accordingly, Linnæus makes it a precept41, that the name of the Class and the Order must not be expressed but understood: and hence, he says, Royen, who took Lilium for the name of a Class, rightly rejected it as a generic name, and substituted Lirium, with the Greek termination.
Yet we must not too peremptorily assume such maxims as these to be universal for all classificatory sciences. It is very possible that it may be found advisable to use three terms, that of order, genus and 136 species, in designating minerals, as is done in Mohs’s nomenclature; for example, Rhombohedral Calc Haloide, Paratomous Hal Baryte.
It is possible also that it may be found useful in the same science to mark some of the steps of classification by the termination. Thus it has been proposed to confine the termination ite to the Order Silicides of Naumann, as Apophyllite, Stilbite, Leucite, &c., and to use names of different form in other orders, as Talc Spar for Brennerite, Pyramidal Titanium Oxide for Octahedrite. Some such method appears to be the most likely to give us a tolerable mineralogical nomenclature.
Sect. VII.—Diagnosis.
20. German Naturalists speak of a part of the general method which they call the Characteristik of Natural History, and which is distinguished from the Systematik of the science. The Systematick arranges the objects by means of all their resemblances, the Characteristick enables us to detect their place in the arrangement by means of a few of their characters. What these characters are to be, must be discovered by observation of the groups and divisions of the system when they are formed. To construct a collection of such characters as shall be clear and fixed, is a useful, and generally a difficult task; for there is usually no apparent connexion between the marks which are used in discriminating the groups, and the nature of the groups themselves. They are assumed only because the naturalist, extensively and exactly acquainted with the groups and the properties of the objects which compose them, sees, by a survey of the field, that these marks divide it properly.
The Characteristick has been termed by some English Botanists the Diagnosis of plants; a word which we may conveniently adopt. The Diagnosis of any genus or species is different according to the system we follow. Thus in the Linnæan System the Diagnosis of the Rose is in the first place given by its Class and Order: it is 137 Icosandrous, and Polygynous; and then the Generic Distinction is that the calyx is five-cleft, the tube urceolate, including many hairy achenia, the receptacle villous42. In the Natural System the Rose-Tribe are distinguished as being43 ‘Polypetalous dicotyledons, with lateral styles, superior simple ovaria, regular perigynous stamens, exalbuminous definite seeds, and alternate stipulate leaves.’ And the true Roses are further distinguished by having ‘Nuts, numerous, hairy, terminated by the persistent lateral style and inclosed within the fleshy tube of the calyx,’ &c.
It will be observed that in a rigorous Artificial System the Systematick coincides with the Characteristick; the Diataxis with the Diagnosis; the reason why a plant is put in a division is identical with the mode by which it is known to be in the division. The Rose is in the class icosandria, because it has many stamens inserted in the calyx; and when we see such a set of stamens we immediately know the class. But this is not the case with the Diagnosis of Natural Families. Thus the genera Lamium and Galeopsis (Dead Nettle and Hemp Nettle) are each formed into a separate group in virtue of their general resemblances and differences, and not because the former has one tooth on each side of the lower lip, and the latter a notch in its upper lip, though they are distinguished by these marks.
Thus so far as our Systems are natural, (which, as we have shown, all systems to a certain extent must be), the Characteristick is distinct both from a Natural and an Artificial System; and is, in fact, an Artificial Key to a Natural System. As being Artificial, it takes as few characters as possible; as being Natural, its characters are not selected by any general or prescribed rule, but follow the natural affinities. The Botanists who have made any steps in the formation of a natural method of plants since Linnæus, have all attempted to give a Diagnosis corresponding to the Diataxis of their method.