Reference has already been made to the anatomical features of leaves of this species described by Lignier[587] and other authors.
The leaves so named by Lesquereux[588], from the Coal Measures of Pennsylvania, are distinguished by the elongate cuneate lamina, which reaches a length of 38 cm. with a narrow base and a slightly rounded truncate distal end, 16 cm. broad, characterised by a few broad and shallow crenulations. By contrast with some American specimens in Dr Kidston’s collection Lesquereux’s figures convey an imperfect idea of the size of the leaf. A large leaf from the Coal Measures of Belgium described by Cambier and Renier as a new species of Psygmophyllum, P. Delvali[589], is perhaps identical with the American type; the lamina of sub-triangular form has approximately the same dimensions; the veins are numerous and repeatedly forked. The leaf is much longer than any known Psygmophyllum and the veins are much more numerous than in P. majus Arb.[590], the largest representative of that genus. Palaeobotanists who have seen the type-specimen inform me that they have no doubt as to the Cordaitean nature of the Belgian specimens, which may be designated Cordaites Delvali. It is, however, not impossible that Psygmophyllum and Cordaites are allied genera: our knowledge of the former is limited to unimportant characters.
This Permian type, originally described by Goeppert[591] as Noeggerathia palmaeformis, is characterised by numerous slender veins: according to Weiss[592] there may be as many as 3–5 in 1 mm. The leaf is broadly lanceolate; it tapers gradually to an acute apex reaching a length of 80 cm. and a breadth of 10 cm. In habit the young foliage-shoots[593] resemble those of C. principalis and C. borassifolius. Grand’Eury records the frequent association of Samaropsis seeds with this species; it occurs in Upper Carboniferous and in Permian strata and is recorded from a few British localities.
Weiss[594] first figured this species from drawings supplied by Goldenberg at whose suggestion the name C. microstachys was adopted. The type-specimen consists of a slender axis bearing numerous narrow linear leaves and a few imperfect fertile axillary shoots. A specimen is figured by Kidston[595] from the Upper Coal Measures of Radstock: it is a rare type in Britain. The species is readily distinguished from C. principalis and similar forms by the narrow lamina which varies considerably in length, rarely as long as 30 cm. and not exceeding 1 cm. in breadth. The apex is obtuse and the ribs are either equal in strength or 1–2 finer striae may alternate with the stronger ribs. The base of the lamina is 3–4 mm. wide and the leaf-scars have a slightly arched upper margin and an almost straight lower edge[596]. The foliage of this species, generally regarded as identical with C. linearis Grand’Eury, bears a close resemblance to that of the Mesozoic genus Phoenicopsis from which it is distinguished by the occurrence of the leaves in bunches.
C. gracilis Lesq.[597] is a similar type. The shoot on which Lesquereux founded his genus Desmiophyllum[598] may perhaps be an example of Poa-Cordaites. Poa-Cordaites tenuifolius Schmal.[599] from the Permian of Russia may be identical with C. microstachys.
As examples of other forms of leaf referred to Cordaites, though as in other cases without any proof of connexion with branches having the anatomical features of the genus, reference may be made to Cordaites circularis Grand’Eury[600] from Gard (fig. 468, B) and a smaller leaf from the same locality compared with C. Lacoei (fig. 468, C) Lesq. Cordaites circularis is characterised by the almost orbicular lamina traversed by slightly spreading veins; it recalls some of the larger Cyclopteris pinnules of Pteridosperm fronds and is indistinguishable from some leaves assigned to the genus Dolerophyllum[601].
The species C. Lacoei was founded by Lesquereux[602] on some detached specimens 3–12 cm. long and 1·5–5 cm. broad; it is by no means certain that a specimen referred by Grand’Eury[603] with some hesitation to this species is Cordaitean.
The generic name Scuto-Cordaites was proposed by Renault[604] for a specimen from Commentry consisting of a flattened branch bearing a few imperfectly preserved leaves. The surface of the branch shows semicircular leaf-scars on decurrent, spirally disposed leaf-cushions and bears a certain resemblance to a slender stem of a Clathrarian Sigillaria. The leaves of the type-specimen of Scuto-Cordaites Grand’Euryi appear to be broadly linear, 13 cm. long, the breadth gradually increasing from the base: a short distance from the proximal end the lamina is broken up into narrow segments; the veins are ·5 mm. apart with finer striations between them.
Some specimens from Pennsylvania made by Dawson[605] the type of a new sub-genus and named Dictyo-Cordaites Lecoi agree in shape and arrangement with some species of Cordaites, but differ in an occasional anastomosis of the veins as in Psygmophyllum flabellatum. It is, however, impossible to determine the true nature of the fossils from the published figures.
In 1845 Goeppert[606] instituted the species Noeggerathia aequalis (fig. 469) and N. distans for incomplete broadly linear and obovate leaves, from Siberian Permian strata, having a contracted base and equal parallel veins. The specimens so named are no doubt specifically identical. Goeppert’s species N. aequalis has recently been carefully investigated by Zalessky[607] who agrees with Kosmovsky[608] in identifying it with Noeggerathiopsis Hislopi (Bunb.) and Rhiptozamites Goepperti Schmal. Schmalhausen[609] had previously pointed out the probable identity of his species with Noeggerathia palmaeformis Goepp. (= Cordaites). The question of specific identity of these leaves from different localities and of other hardly distinguishable forms is of secondary importance; the main point is that they are all examples of Cordaitean leaves, Cordaites or some allied genus, and point to the existence of this group of Gymnosperms during Permo-Carboniferous times in Siberia, China, India, Australia, South Africa, and S. America, also in the Rhaetic floras of Tonkin[610] and Mexico[611]. The fragments from Devonian strata at Iguana Creek, Australia, named by McCoy[612] Cordaites australis are probably pieces of the rachis of some large frond.
Wieland[613] recently discovered Cordaitean leaves exhibiting a wide range in size and shape in the Mixteca flora of Mexico in the lower members of a series which extends from the ‘upper borders of the Rhaetic’ through the Liassic to the lower beds of the Inferior Oolite. These leaves are referred to Noeggerathiopsis Hislopi, and it is clear from an examination of photographs received from Dr Wieland, one of which is reproduced in fig. 470, that the Mexican Cordaites cannot be specifically distinguished from Bunbury’s type as represented by specimens described from India, South Africa, Siberia, Tonkin, and elsewhere.
The occurrence of Noeggerathiopsis is also recorded by Newberry from the Rhaetic series of Honduras[614].
Noeggerathiopsis. This genus was founded by Feistmantel[615] for some leaves from Lower Gondwana rocks in India originally described by Bunbury[616] as Noeggerathia (Cyclopteris?) Hislopi (figs. 470–472) and regarded by him as probably Cycadean. Several authors have added to our knowledge of this widely spread southern type and in many localities the leaves occur in association with platyspermic seeds of the Samaropsis or Cordaicarpus type, pieces of stems with Cordaitean leaf-scars, and petrified wood agreeing in the structure of the secondary xylem with that of European species of Cordaites. In some Permo-Carboniferous sandstones at Vereeniging, South Africa, stumps and spreading roots (fig. 478) resembling those described from France by Grand’Eury (cf. fig. 468, A) have also been discovered. A remarkable occurrence of roots and prostrate stems of some forest-tree was recorded some years ago in the bed of the Vaal river near Vereeniging where the surface of a seam of coal was exposed over an area of more than two acres[617]. Large branched roots (fig. 478) spreading over the coal for a distance of several feet and thick stems 40–50 ft in length with very few branches and but little decrease in diameter afford a striking picture of a forest-floor. The frequent occurrence of Cordaites (Noeggerathiopsis) Hislopi in the associated strata suggests a reference of the stems and roots to that species. Moreover the structure of the secondary xylem of some petrified pieces of stem sent to me by Mr Leslie from Vereeniging agrees closely with that of a European Cordaitean stem.
The leaves of Cordaites (Noeggerathiopsis) Hislopi vary considerably in size, in some cases reaching a length of 80 cm. (fig. 471); the lamina tapers gradually from a short distance behind the obtuse apex to a relatively narrow base: in venation and form the leaves are very similar to those of C. principalis and other European and North American species. The specimen from India represented in fig. 472 shows several spathulate leaves attached in a close spiral to a branch. As White[618] and Zalessky have shown, the stronger ribs are separated by less prominent striations indicating the presence of two sizes of hypodermal strands. The obvious resemblance between Noeggerathiopsis Hislopi and species of Cordaites has long been recognised and many authors have included Feistmantel’s genus in the Cordaitales[619]. Prof. Zeiller[620] preferred to retain the name Noeggerathiopsis as a precautionary measure, chiefly on the ground that the stomata appeared to be less definitely arranged in rows and more scattered than in the European leaves of Cordaites, and because of the absence of interstitial veins. We have as yet little information as to the arrangement of the stomata, but in view of the irregularity in stomatal grouping in recent leaves this feature is, perhaps, of minor importance. The presence of interstitial ‘veins’ has now been established in Indian[621] and South American[622] leaves. In a paper published in 1908[623] the name Cordaites was substituted for Noeggerathiopsis and Zalessky’s recent work supports this step. The description by Zalessky of the ribbing in Goeppert’s species Cordaites aequalis from Siberia shows how uncertain and variable a character the venation is even in different parts of the same leaf.
This species (fig. 469, D) was instituted for some small lanceolate or spathulate leaves from the Petschora basin (Adzva River)[624] reaching a length of 6 cm. and a breadth of 1 cm. It is separated from Cordaites aequalis on the ground that the veins are more numerous, as many as 44 in a breadth of 1 cm.
A recent investigation by Miss Holden[625] of the carbonised cuticles of some Indian specimens, sent to Cambridge by the Director of the Indian Geological Survey, and a comparison of them with preparations made from European Cordaites leaves, have revealed certain distinguishing features which support Zeiller’s view that the Gondwana-Land leaves, though similar superficially to those of Cordaites, are probably distinct. It is, however, impossible in many cases to obtain any information with regard to epidermal characters, and though it would seem probable that had we a fuller knowledge of the Indian and southern hemisphere plants represented for the most part by leaf-impressions well-defined distinguishing features would be recognised, the comprehensive name Cordaites may conveniently be retained on the ground that in the absence of well-preserved cuticles no satisfactory distinguishing features are exhibited by the impressions of Noeggerathiopsis.
Zalessky[626] founded this genus on some Permian leaves from the Petschora basin (Adzva River) which closely resemble those of Cordaites but are characterised by a coarser venation. The lanceolate lamina reaches a length of 18 cm. and a breadth of 4·2 cm.; the veins are 2 mm. apart and occasionally forked near the base of the leaf. The epidermal cells have straight walls and stomata are abundant on the lower surface. As Zalessky says, the systematic position of the leaves is uncertain though they are probably Cordaitean. The coarseness of the venation is a feature of minor importance and hardly worthy of generic recognition.
This genus was instituted by Schmalhausen[627] for leaves from beds in the Kusnezk basin regarded by him as Jurassic. These strata are now recognised as Permian[628] and homotaxial with those from which Schmalhausen[629] subsequently recorded the same species. The leaves, though smaller than many of the Indian and South African specimens of Cordaites (Noeggerathiopsis) Hislopi, may belong to that species. Zeiller and others definitely assigned the Russian leaves to Cordaites.
Euryphyllum. The Indian leaves for which Feistmantel[630] proposed this name are, as several writers have pointed out, in all probability referable to Cordaites.
The general conclusion to be drawn from this imperfect summary of an extensive literature is that the employment of the generic names Noeggerathiopsis, Rhiptozamites, Euryphyllum, and others has tended to exaggerate the difference between the European and Southern botanical provinces during the Permo-Carboniferous period.
The occurrence of small scale-like leaves of the type represented in fig. 468, C, in association with Cordaites (Noeggerathiopsis) Hislopi[631] in India, Brazil, Siberia, and elsewhere may mean that these organs are scales of large foliar buds. The occurrence of several forms of platyspermic seeds, in some cases apparently identical with European forms and sometimes distinct types, in close association with Cordaites (Noeggerathiopsis) Hislopi has already been mentioned. Examples of such seeds are described in Chapter xxxv. under the genus Samaropsis.
There are very few satisfactory examples of Cordaitean branches from the southern hemisphere. Schmalhausen[632] figures good specimens from Siberian rocks from which his Rhiptozamites leaves were obtained. Branches with spirally disposed leaf-scars figured by Zeiller[633] from the Rhaetic of Tonkin closely resemble Cordaicladus. Feistmantel’s drawing of a fossil from the Karharbari series, compared by him with a Fern rhizome[634], may be a Cordaitean branch, and the same author describes a stem[635] from New South Wales as Caulopteris Adamsi which bears a close resemblance to a branch of Cordaites. Similarly a leafy shoot described from India by Zeiller as Araucarites Oldhami[636] may be compared with branches of the Poa-Cordaites type.
A character to which authors tend to attach excessive importance as a diagnostic feature is the almost invariable tendency of the parenchymatous pith of Cordaites to break up on contraction into transverse diaphragms, thus producing what is known as a discoid pith. In the stem shown in fig. 473 the pith is represented by a more or less cylindrical cast characterised by fairly regular transverse ribs and narrow grooves; in the upper part of the fossil the peripheral tissue of the pith is preserved in the form of narrow plates projecting from the inner face of the wood. As Renault[637] pointed out, this type of pith is the expression of certain conditions of growth and is not a satisfactory distinguishing feature of any particular genus or family. The same tendency to form a discoid pith is characteristic of Mesoxylon, and it occurs also in some other Palaeozoic genera. Corda long ago figured a stem attributed by him to Lomatofloyos with a typical discoid pith, and a similar pith is recorded in a stem of Dicranophyllum[638]. Among recent plants Juglans regia affords perhaps the most familiar instance of an identical form of pith: the same type occurs in the white Jasmine, in Ceropegia peltata, and some other flowering plants. An interesting case is that of the tree Groundsel, Senecio praecox D.C.[639], of Mexico: in this plant, which grows in arid districts, the pith serves as a water-store and as the water is drawn off the thick turgescent discs contract and form thin transverse diaphragms separated by wide spaces, as is also the case on drying in some succulent Euphorbia stems. It may be that in Cordaites the medullary region also served as a water-reservoir and the depth of the medullary discs would vary according to the state of their contents.
The earlier writers regarded the pith-casts as stems with scars of amplexicaul leaves: Artis[640] described specimens from the English Coal Measures as Sternbergia, one of which he stated to be 6 ft long; a few years later Sternberg[641] proposed the name Artisia and this has been generally used on the ground that Sternbergia is the name of a recent flowering plant. A specimen of Artisia transversa (Art.) from the Coal Measures of Yorkshire is shown in fig. 466, B, and similar specimens varying considerably in diameter up to about 10 cm. are abundant in European and American Coal Measures. The prominence and depth of the transverse ridges, the presence or absence of anastomoses between adjacent discs are, as Zeiller[642] says, of very doubtful value as specific characters. Dawson in 1846[643] spoke of Artisia as probably the pith of a tree, a view suggested to him by Mr Dawes. In 1851 Williamson[644] published a description of some specimens in which a pith-cast, Artisia approximata Lind. and Hutt., was enclosed by wood showing very clearly Cordaitean characters. Further demonstration of the true nature of Artisia was supplied by Grand’Eury from St Étienne material. If the generic name Artisia is applied to all pith-casts showing the transverse ridges and grooves like those seen in fig. 466, B, it must be remembered that it is not safe to assume a connexion with Cordaites or Mesoxylon. A Liassic species described by Lignier[645] from France as Artisia alternans is quoted by authors as evidence of the persistence of Cordaites into the Jurassic period; but in view of the fact that the discoid type of pith is not by any means confined to Cordaites or even to the Cordaitales the occurrence of Artisia is in itself of no great botanical significance.
It is also true that a discoid pith is not an invariable attribute of stems closely allied to the genus Cordaites; but if these reservations are made the use of the generic term Artisia serves a useful purpose.
Palaeobotanical literature contains numerous descriptions of Palaeozoic petrified wood occasionally enclosing an Artisia pith-cast described under such names as Dadoxylon, Cordaioxylon, Araucarioxylon, etc., and regarded as portions of Cordaitean stems. It is, however, certain that much of this material belonged to stems other than those of Cordaites. Recent research has demonstrated the insufficiency of the secondary xylem alone, however well preserved, as a safe guide to generic position: stems identical in the structure of the secondary xylem differ in that of the primary portion of the stele, and it is on the characters of the latter tissues that several genera have recently been founded. Mesoxylon affords a striking example of the importance of the primary xylem as a distinctive feature. As Gothan[646] points out, the species of Calamopitys recently made the type of a new genus Eristophyton[647] would, in the absence of the primary xylem, probably be regarded as Cordaitean. It is important to recognise the limitations imposed by the imperfection of the material; we cannot in most cases determine whether a specimen should be referred to Cordaites or Mesoxylon, and while it may be described as probably Cordaitean in affinity there remains the possibility that some of the Palaeozoic plants with secondary wood like that of Cordaites, if their reproductive organs were known, would not be included in the Cordaitales. Goeppert’s species Araucarites Tchihatcheffi, which Renault[648] quotes as Cordaites, has recently been assigned to a new genus Mesopitys[649] because of certain distinctive features of the primary xylem. Additional examples might be quoted pointing to the tendency of recent and more thorough investigation to establish the fact that the occurrence of Permo-Carboniferous wood of the Araucarian type does not necessarily denote the existence of Cordaites. The question of nomenclature is necessarily raised in this connexion.
In recent years it has been customary to assign Palaeozoic wood with Araucarian pitting to the genus Dadoxylon, while wood of the same general type from more recent strata is by many authors referred to Araucarioxylon[650]. This arbitrary distinction based on a difference in age is open to serious objection. Fossil wood of the Araucarian type is widely scattered in strata ranging from Carboniferous to Jurassic periods; it also occurs in later formations. The fact that on the one hand Araucarian plants, as recognised by cones and foliage-shoots, are especially characteristic of Jurassic floras and occur more rarely in Rhaetic and Triassic floras, and on the other hand that Cordaites and its allies reached their greatest development in Permo-Carboniferous times, renders it probable that in the majority of cases a distinctive name based on geological age would be in accordance with botanical differences. But we have no satisfactory data as to the upper limits of the Cordaiteae or the lower limits of the Araucarineae: in all probability the two families overlapped and co-existed for more than one geological period. It is, moreover, the plants from formations where overlapping occurred that are the most critical from a botanical standpoint. The age-distinction is therefore at best an artificial one and may be seriously misleading. Potonié[651] and Gothan[652] have emphasised the desirability of adopting the name Dadoxylon for all wood of the Araucarian type irrespective of age. If a particular specimen can be correlated definitely with Cordaites or some other genus it should be so designated, but the fragmentary nature of the records usually precludes this simple course. The most logical plan is to use the name Dadoxylon for all woods with Araucarian characters if there is no sufficient reason for employing a less provisional term. If the evidence clearly points to the Araucarineae the generic name Araucarioxylon should be added in parentheses after Dadoxylon, but whether or not this is done, a statement as to the geological age of the fossil will in itself be some assistance in enabling the student to form an opinion on the balance of probability in favour of a Cordaitean or an Araucarian affinity. The course suggested by Gothan[653], namely to add Cordaites after Dadoxylon if an Artisia pith is present, is rendered inoperative now that we know that a discoid pith occurs in more than one genus. In this chapter we are concerned primarily with Cordaites and with such stems as may fairly be regarded as Cordaitean: examples of fossil wood from later formations are dealt with in another place. A distinction between Araucarioxylon and Cordaioxylon stems has been based by Felix on the nature of the pith-casts; those of the Artisia type he refers to Cordaioxylon, while Palaeozoic stems with Tylodendron pith-casts are assigned to Araucarioxylon[654]. This distinction can, however, only be made in the comparatively few cases in which the pith-cast is preserved. Its validity is, moreover, open to question. A Tylodendron (= Schizodendron) cast shows on its surface the characters of the inner face of the secondary xylem, projecting spindle-shaped areas representing the inner ends of medullary rays and a reticulum of grooves formed by the more resistant and prominent inner edges of the rows of tracheids (fig. 746). A pith-cast of a stem in which the destruction by decay of the medullary parenchyma had not extended to the edge of the xylem-cylinder might show transverse diaphragms. The occurrence of Tylodendron casts means that decay had extended to the surface of the wood. But in view of the occurrence of Tylodendron casts in stems that are not those of Cordaites a short account of the genus is given on another page[655].
The main features of the stem of Cordaites have already been enumerated. The stele agrees with that of Araucaria and Agathis and especially with Agathis in the double nature of the leaf-trace. Williamson[656] in 1877 described pieces of wood from the English Coal Measures and the Lower Carboniferous of Scotland which he referred to Dadoxylon but without any specific name. These include the Coalbrookdale stem in which he had previously demonstrated the connexion between Artisia and Dadoxylon. The structure of the xylem is like that in D. Brandlingii and the specimens may belong to that species. The most interesting fact recorded by Williamson is the occurrence of double leaf-traces, a feature which led him to suspect a remote generic affinity to Ginkgo. This double trace may be an important diagnostic feature but unfortunately the majority of descriptions of species of Dadoxylon throw no light on the character of the foliar bundles.
Thomson and Allin[657] have recently pointed out that a double leaf-trace occurs in a stem from the Permian of Kansas described by Penhallow[658] as Pityoxylon chasense and referred to that genus because of the supposed occurrence of resin-canals in some of the medullary rays: the canals are apparently leaf-traces traversing broad rays in the secondary wood.
The primary xylem of Cordaites is in direct continuity with the secondary tracheids and does not form mesarch strands as in Mesoxylon. The pith is usually discoid. The pitting on the tracheids is a character of special importance: while it is true to say that as a rule the number of pits on the radial walls of a single tracheid is larger than in the Araucarineae, this is not always the case. In Araucaria there are occasionally as many as five rows of alternate polygonal pits (fig. 691, A) and in some Palaeozoic Dadoxylons there are only one[659] or two rows. The very broad zone of transitional elements at the inner edge of the xylem-cylinder is a characteristic feature shared by the Araucarineae[660]; the spiral protoxylem-tracheids are succeeded by scalariform elements and these, by the gradual anastomosing of the transverse bars, pass into tracheids with multiseriate pitting. In this broad zone we probably have a primitive feature, an epitome in a single stem of the course of development of multiseriate from scalariform pitting. In some Palaeozoic species with wood of the pycnoxylic type and agreeing generally with typical Cordaites the bordered pits are sometimes separate and circular, and opposite pits occasionally replace the usual alternate arrangement. Another feature on which stress has been laid is that in Cordaites the pits occupy the whole breadth of the tracheal wall; but this, though frequently the case, is by no means a constant feature. In Dadoxylon Newberryi[661] the pits tend to form groups, leaving unpitted areas, as in the genus Coenoxylon[662]. In the stem of Dadoxylon materiarum Daws. represented in fig. 475 the pits do not always cover the whole of the tracheid-walls: this stem is also instructive as an example of the different appearance presented by pitted tracheids according to the state of preservation. In some places an oblique pore is well shown while in others only the outer border of the pit is seen. Gothan[663] has described a specimen in which some of the pits are circular and occupy only the central area of the xylem elements: separate circular pits occur also in D. Pedroi Zeill.[664] (fig. 476). Similar departures from the normal are illustrated by recent species of Araucarineae. The absence of a torus is another feature shared by Dadoxylon and true Araucarian wood. Annual rings other than incomplete and spasmodically formed rows of narrower tracheids are not as a rule present, and in this respect also Araucaria affords a close analogy. Thomson[665] has figured a transverse section of a root from English Coal Measures in which rings of growth are well defined; and other instances are recorded. In an Australian species named by Arber D. australe[666], there are well-marked rings of growth, and this is equally the case in some Indian wood[667] of Permo-Carboniferous age, more nearly allied to Mesoxylon than to Cordaites, and in a Dadoxylon of similar age from South Africa. On the other hand the statement that annual rings occur in Palaeozoic wood is often incorrect, partial rings having been confused with regular concentric cylinders of summer elements. Dawson and Matthew[668] described rings in D. ouangondianum, and Goeppert and Stenzel[669], who examined the Canadian material, refer to circles like annual rings; but Penhallow[670] states that there is no evidence of true growth-rings.
The medullary rays are uniseriate and consist of thin parenchymatous cells with unpitted walls; they vary considerably in depth, usually comparatively shallow but in some cases 40 or 50 cells deep. In recent Araucarineae the rays are generally shallower. The absence of special receptacles, other than occasional resiniferous tracheids, for products of secretion is a feature common to Dadoxylon and the Araucarineae. The phloem presents no features of special interest, but our knowledge of this tissue is comparatively meagre.
Among other examples of large Dadoxylon stems some of which no doubt bore Cordaitean foliage—though as a rule we have insufficient information as regards anatomical characters to enable a decision to be made between Cordaites and Mesoxylon—reference should be made to the imposing array of silicified trunks in the grounds of the Chemnitz Museum[671]. These were obtained from Lower Permian strata at Hilbersdorf near Chemnitz from beds overlain by porphyry tuff and resting on quartz porphyry, the volcanic material which furnished the siliceous solutions. Several large pieces of wood were found in association with stems of Medullosa and Psaronius, leaves of Cordaites, Artisia pith-casts, and Cardiocarpus seeds with specimens of Walchia, Gomphostrobus and other plants. Sterzel describes a stem 16·5 met. long and 1·5 met. in diameter; on the main trunk the branch-scars are scattered but on some branches there is a tendency to a whorled arrangement. This and many other stems are referred to Araucarioxylon (or Dadoxylon) saxonicum, a species first described by Reichenbach as Megadendron saxonicum. In one specimen Sterzel states that the bordered pits are generally in 1–2 rows, though rarely in 3–4 rows, on the radial walls of the tracheids which they do not completely cover: the medullary rays reach a depth of between 20 and 30 cells. It is noteworthy that the stem 16·5 met. long has a pith-cast of the Tylodendron type.
| 1831. | Pinites Brandlingii Lindley and Hutton, Foss. Flor. Vol. i. Pl. i. |
| 1850. | Araucarites Brandlingii Goeppert, Foss. Conif. p. 232, Pls. xxxix.–xli. |
| 1890. | Cordaioxylon Brandlingii Schenk, in Schimper and Schenk, p. 853, fig. 408. |
This species was founded on ‘a fossil giant of the vegetable kingdom’ discovered at Wideopen near Newcastle in Carboniferous strata on the estate of Mr Brandling. The stem, 72 ft long and far from complete, showed an irregular and not a whorled distribution of branch-scars. It is noteworthy that in D. medullaris (Goepp.)[672], a Permian species from Saxony, the branch-scars, while for the most part irregularly scattered, in one case showed an approach to a whorled disposition as in recent Araucarias. Witham[673] gave a fuller account of the structure of the stem than is included in the original description, and the species has been described by many later authors from both Permian and Carboniferous localities. The pith is discoid and the broad transitional region at the inner edge of the wood is a characteristic feature[674]. Thomson[675] points out that there is a tendency to a retention of the scalariform type of pitting in the region of the medullary rays. There are 1–5 rows of pits on the radial walls of the tracheids. The rays may reach a depth of 40 cells; they are usually one cell broad. It has recently been shown that as many as six vascular strands[676] may form one leaf-trace instead of the customary pair, a feature suggesting comparison with Metacordaites Rigolloti Ren. with its five foliar bundles. Other species agree very closely with D. Brandlingii and it is impossible to determine with accuracy the precise specific limits of stems agreeing generally with this type; but for the sake of emphasising the variation in anatomical structure it is worth while to draw attention to a few more or less divergent forms from different geographical areas.
An interesting feature in this Westphalian type from Germany is the occurrence of transversely elongated pits on the tracheids[677] associated with those of normal form closely simulating the pits in the xylem elements of Protopitys.
In this Brazilian wood[678] from Permo-Carboniferous beds the medullary rays are very numerous, mostly uniseriate and 1–30 cells in depth. The pits on the tracheids are in 1–2 rows and are often contiguous. In another type, D. meridionale, described by the same author[679], the pits are strictly uniseriate and generally contiguous. As White says, the absence of the pith and cortex and of any evidence as to the structure of the primary xylem renders impossible any definite expression of opinion as to the affinity of these and many other species.
Dr Arber[680] in naming this species, from the Newcastle (Permo-Carboniferous) Series of New South Wales, Dadoxylon australe, does not mention Crié’s earlier account of some wood from New Caledonia under the name Araucarioxylon australe[681]. The latter generic name according to the usage adopted in this volume should be superseded by Dadoxylon, and this necessitates a fresh specific name for Arber’s specimens. The name Nicoli is suggested in place of australe, as the sections on which Arber founded his species form part of the Nicol collection in the British Museum.
The xylem shows distinct rings of growth, a feature also seen in Indian stems of approximately the same geological age and recorded by Shirley[682] in wood from Queensland which needs more careful examination. The bordered pits, usually multiseriate and contiguous, are not infrequently in 1–2 rows and separate. The uniseriate medullary rays are very numerous as in White’s Brazilian species D. nummularium, and as a rule 6–12 cells deep. Some well-preserved specimens from Permo-Carboniferous strata in Natal and Zululand have been described by Warren[683] as Dadoxylon australe Arb., showing interesting anatomical features, but the material almost certainly includes more than one specific type and would repay more detailed investigation.
This species was described by Dawson[684] from Carboniferous strata in Nova Scotia and afterwards referred by Penhallow[685] to the genus Cordaites. In the transverse section reproduced in fig. 474, A, the tracheid-walls have been reduced in thickness by partial decay, but some of the bordered pits are clearly shown on the radial walls; the pits usually form 2–4 contiguous rows (fig. 475) in some cases with an oblique pore while others are represented either by the outer border of the pit or by the pore only. The narrow medullary rays are as a rule uniseriate and may be 60 cells deep (fig. 474, B). Dawson states that some specimens have large Artisia pith-casts, a fact that formerly would have been regarded as proof of the Cordaites nature of the wood, but in the absence of evidence with regard to the nature of the primary xylem it is impossible to say whether the stem is Cordaites or Mesoxylon.
Some wood received from Mr Leslie, collected at Vereeniging, South Africa, in Permo-Carboniferous rocks, shows well-defined rings of growth. The pits form either a single row, a double, alternate and contiguous row, or rarely three series on the tracheid walls. The medullary rays are usually uniseriate and 1–30 cells deep.
This species is represented by some large trunks, in some cases with a diameter of 40 cm., discovered by Mr Kay in the Coal Measures of Worcestershire[686]. The pith is very small and shows no indication of a discoid structure, but owing to its poor preservation no sections could be obtained of this region. The secondary wood is characterised by the large number of uniseriate medullary rays 1–27 cells in depth; the tracheids have usually two or sometimes three rows of alternate and contiguous bordered pits on the radial walls. Arber regards the absence of a discoid pith as a fatal objection to a reference of the stems to Cordaites and speaks of them as affording further evidence of the occurrence of Coniferae in the higher Coal Measures of the Midlands. It is, however, impossible to determine the position of the species in the absence of any data with regard to the structure of the perimedullary region, and without such information we are hardly justified in regarding Dadoxylon Kayi as a member of the Coniferales.