CARBONIFEROUS LYCOPODS AND SPHENOPHYLLS. 51 



Lycopodium. 1 If we add to this the presence of a ligule on the 

 leaves (?) of Lepidodendron and on the sporophylls of Lepidostrobus 

 (and as far as I can judge from the investigations of Bertrand, 

 Hovelacque, and Maslen, the cushions of Lepidodendron and 

 sporophylls of Lepidostrobus possess a small scale), then the 

 position of Lepidodendron points to a closer relationship with 

 Selaginella than with any other existing genus. 



Though I have seen the so-called ligule in transverse sections 

 of leaf-bases, or cushions as they have been usually termed, as 

 figured by Hovelacque, 2 I have not seen it in profile as figured 

 in Lepidostrobus by Maslen. 3 



As already mentioned, if we regard the small point above the 

 leaf-scar as the cicatricule, or, more correctly, the opening of the 

 ligule cavity, we must consider what has usually been termed the 

 leaf-cushion as a persistent part of the leaf, and not a cortical 

 outgrowth. In Lepidodendron the " leaf -cushion " is generally 

 clearly circumscribed, and one can imagine it to be the very much 

 shortened portion of a persistent leaf-base, though I do not know 

 of any other plant that sheds part of the leaf while the remaining 

 portion persists as a cushion on the bark. 4 



When, however, one applies the same explanation in regard to 

 the " ligule-scar " of Sigillaria, and I presume there is no doubt 

 that the small cicatrice so frequently seen a short distance above 

 the leaf-scar is homologous to the so-called ligule-scar in Lepido- 

 dendron, additional difficulties arise in explaining its position as 

 representing the ligule of Selaginella. 



In Sigillaria there is no "field" surrounding the leaf -scar, or 

 any other mark to define an area corresponding to the field in 

 Lepidodendron, and still we must presume here also that the 

 "ligule-scar" on Sigillaria is placed on the leaf-base if the 

 homology is to hold good, for if it is not on the leaf-base, but on 



1 Perhaps, however, too much importance is being placed on the hetero- 

 sporous and homosporous condition in the classification of the recent 

 Lycopods. 



2 Becherches sur le Lepidodendron selaginoides, Sternb., PI. VII., fig. 2. 



3 Maslen, Annals of Botany, Vol. XII., 1898, p. 258. 



4 In many species of Lepidodendra the leaf when shed leaves behind so 

 clearly defined a scar, that I think one must conclude that the leaf has been 

 cut off by some structure specially adapted to perform this function. 



