c. Bothrodendron kiltorkense (Haughton). Fig. 212, G, H.

The specimens from the Upper Devonian rocks of Co. Kilkenny on which Haughton founded this and two other species may be regarded as representing one specific type. He described the circular leaf-scars as arranged in alternating whorls. In habit the Irish species agrees with Bothrodendron minutifolium, but the leaf-scars are more elliptical ([fig. 212], H) and the ligule-pit is usually absent. The leaf-scar shown in fig. H is 1·2 mm. broad and 1·4 mm. in height. The large collection obtained during the visit of a Swedish expedition to Bear Island in 1898 under the leadership of Dr Nathorst has materially increased our knowledge of this ancient type. The form of the leaf-scars varies according to the age of the branch and their disposition is far from constant even on the same specimen; in some cases the scars are in fairly regular whorls ([fig. 212], G; an Irish specimen) while in others they are in regular spirals. This irregularity of arrangement, which is well illustrated by Nathorst’s figures of Bear Island and Irish specimens, finds its counterpart, though in a less marked form, in recent species of Lycopodium, e.g. L. Selago. Partially decorticated stems may present a superficial resemblance to Calamites, the fissured bark simulating the ribs of a Calamitean cast. Such stems, as Nathorst has pointed out, were mistaken by Heer for Calamites radiatus. The smaller branches are characterised by a smooth surface, and older shoots resemble Bothrodendron minutifolium in the presence of fine vertical lines. The preservation of only one pit on the leaf-scars of many examples led authors to conclude that the species is peculiar in this respect, but Nathorst has shown that in more perfectly preserved specimens each leaf-scar bears three small dots. A specimen from Ireland in the British Museum[619] illustrates the dichotomous branching and the longitudinal wrinkling of the bark; the leaf-scars are 2 mm. broad and 2·5 mm. deep.

Nathorst[620] has described some examples in which the leaf-scars occur on the lower instead of on the upper end of the leaf-cushions; these and other specimens with obscure surface-features he suggests may be underground axes, comparable in habit with Stigmaria though not identical as regards details. It is pointed out that the absence or scarcity of Stigmaria in the Bear Island beds renders it unlikely that Bothrodendron bore typical Stigmaria branches. F. E. Weiss[621] has recently described root-bearing organs possessing primary xylem identical with that of Bothrodendron mundum; while closely resembling Stigmaria ficoides in certain anatomical characters, they clearly represent a distinct type. This discovery of a Stigmaria-like axis almost certainly belonging to Bothrodendron is consistent with Nathorst’s views on some of the Bothrodendron impressions from Bear Island.

Information as to the cones of this species is restricted to a description by Schimper[622] of a specimen in the Dublin Museum as Lepidostrobus Bailyanus; this has sporophylls with a subtriangular base bearing several megaspores and terminating distally in a slender lamina 12 cm. in length.

An example of a Bothrodendron with more prominent leaf-cushions than those already mentioned is afforded by a species from Bear Island described by Heer[623] as Lepidodendron Wükianum and afterwards referred by Nathorst[624] to Bothrodendron. The same type is recorded also by Schmalhausen[625] from Lower Carboniferous or Devonian strata of Siberia. Certain Scotch specimens from the Calciferous Sandstone, which Kidston[626] referred to Heer’s species, are regarded by Nathorst and, in part at least, by Weiss[627] and Sterzel as representing a distinct species which these authors designate Bothrodendron Kidstoni[628].

Without attempting the hopeless task of discriminating between the various Carboniferous and Devonian specimens described under the names Cyclostigma or Bothrodendron, reference may be made to the following records as illustrating the wide distribution of the genus. Schmalhausen[629] records Cyclostigma kiltorkense from Siberian rocks assigned to the Ursa stage (Devonian or Lower Carboniferous). The fossil described by Dawson[630] from the Devonian of Gaspé as Cyclostigma densifolium probably represents a badly preserved example of Bothrodendron: Weiss’s species Cyclostigma hercynium[631] from Lower Devonian rocks of the Hartz district may be identical with Bothrodendron kiltorkense. The supposed identity of the latter species with Dechenia Roemeriana Goepp., as described by Potonié[632], appears to require confirmation[633], but if this author is correct the connexion demonstrates the continuity of Bothrodendron shoots and Stigmaria-like subterranean organs. The specimens described from South Africa, from strata which may be correlated with the Upper or possibly with the Lower Carboniferous series of Europe, as Bothrodendron Leslei[634] in all probability represents a species closely allied to the Irish and Bear Island type. Bothrodendron Leslei named after Mr Leslie whose discoveries in the Carboniferous Sandstone of Vereeniging (Transvaal) have added considerably to our knowledge of the South African Palaeozoic types, is represented by imperfectly preserved casts characterised by more or less circular scars displaying the same irregularity of arrangement as in Bothrodendron kiltorkense. The leaf-scars appear to have only one small pit, but this may not be an original feature. The identification of this plant as Bothrodendron receives support from the discovery of rather more satisfactory specimens at Witteberg sent to me for examination by Dr Schwarz[635]. These fossils bear a striking resemblance to B. kiltorkense. Cydostigma australe[636] Feist. described from the Lower Carboniferous rocks of New South Wales, though too imperfectly preserved to refer with confidence to B. kiltorkense, is no doubt a closely allied type.

Fig. 214. Bothrodendron Leslei Seward.
b. Natural size.
a, c. Slightly enlarged.