152 FOSSIL PLANTS. 



Phytolithus plantites. 



Martin, Petrificata Derbiensia, pi. xiv. fig. 4. 



Palmacites verucosus. 



Schlotheim, Petrefactenkunde, p. 395, pi. xv. fig. 5. 



Remarks. The synonymy of the various species of Lepidodendron is 

 extremely difficult, on account of the great change that takes place in the 

 form and dimensions of the leaf -scar as the plant increases in size and age. 

 This circumstance has not always been sufficiently kept in view, and conse- 

 quently many species have been created whose supposed specific characters 

 are entirely dependent on the age of the specimen, and not on real structural 

 differences. 



The specimens of Lepidodendron which the Botanist has to examine 

 are invariably mere fragments of a tree which attained the height of 

 100 feet ; hence it is evident in plants whose leaf -scars keep pace in growth 

 with the increase of the stem, and those on older and larger branches will 

 differ considerably from those on the younger twigs, not only in size, but in the 

 relative proportion of their width to their vertical height. In most species 

 the increase in the girth of the stem has a tendency to produce a greater 

 lateral increase in the proportions of the leaf -scars than is equalised by the 

 upward growth of the trunk ; consequently in some species, where the leaf- 

 scars on the young twigs have a vertical length much greater than their 

 width, their older conditions show proportionally a much greater transverse 

 diameter. 



These remarks apply more or less to all species of Lepidodendron, though 

 in some the increase in size of the stem is accompanied by a vertical splitting 

 of the bark, which must to a considerable extent influence the form of the 

 leaf -scar on the older stems, in so far as it probably helps to neutralise the 

 tendency of the leaf-scar to become laterally expanded. 



Geinitz, under his Sagenaria dichotoma, appears to have included in error 

 a specimen of Lepidodendron longifolium (I.e. pi. iii. fig. 1), and two specimens 

 of Lepidodendron rimosum (pi. iii. figs. 10, 11). These I exclude from Lepido- 

 dendron Sternbergii ( = Lepidodendron dichotomum}. Figure 8 of the same 

 plate is also probably referable to Lepidodendron rimosum. 



Lepidodendron obovatum is only a varietal form of Lepidodendron Sternbergii, 

 the apparent differences being consequent on the age of the specimens. 



The exquisite figures given by Ettingshausen in his Steinkohleuflora von 

 Eadnitz (pi. xxvi. figs. 1, 2, pi. xxvii. and pi. xxviii.), as Lepidodendron 

 Sternbergii do not belong to that species, but are the Lepidodendron longi- 

 folium of Brongniart. 



Lepidodendron dilatatum, L. and H., is only a fragment of a stem of Lepi- 

 dodendron Sternbergii, to which the leaf-bases are still attached, though 

 their upper portions have been broken off. 



Lepidodendron gracile, L. and H., and Lepidodendron lycopodioides, Stern- 

 berg, are only the younger branches of Lepidodendron Sternbergii, Brongniart. 

 Lepidodendron selaginoides, Sternberg, also appears to me to be referable to 

 the same species. 



Lycopodites longibracteatus, Morris, which shows portions of an attached 

 cone, is the same state of Lepidodendron Sternbergii as that to which Brong- 

 niart had previously applied the name of Lepidodendron ophiurus. Similar 

 specimens showing the form of the leaf-scars in a state of great perfection 

 are common in the ironstone nodules occurring so plentifully at Coalbrook 

 Dale and in the neighbourhood of Dudley. To a specimen from one of these 

 localities Konig has applied the name of Sagenaria Martini. 



Lepidodendron plumarium, L. and H., is also, I think, to be referred to 

 Lepidodendron Sternbergii as a young and fructifying branch. 



Lepidodendron rugosum does not seem to be specifically distinct from 

 Lepvdodendron Sternbergii, and appears to be similar to the form named 

 Lepidodendron obovatum, by Sternberg, with the addition of a few transverse 



