262 STUDIES IN FOSSIL BOTANY 



The leafless rhizomes of Psilotum and Tmesipteris 

 offer but a poor analogy, for they bear no roots or other 

 appendages, except hairs. The best analogy we can 

 find for the Stigmarian organs is in the rhizophores of 

 Selaginella. These, like the former, are leafless branches, 

 having no other function than to bear the roots ; they 

 may also be regarded as being themselves modified 

 roots. In some cases, as we have seen above (p. 244), 

 their structure shows some slight approximation to that 

 of Stigmaria ficoides. The position of the rhizophores 

 on the stem is, it is true, very different in the two 

 genera, but this is not an insuperable difficulty, for we 

 are not assuming a strict homology, but rather suggest- 

 ing a parallel modification. 



It may be suggested that the terminology most in 

 harmony with the facts would be to call the main 

 axis of Stigmaria a rhizophore, and its appendages 

 roots. Considering, however, that even in existing 

 Lycopods, as notably in Lycopodium itself, the differentia- 

 tion between root and stem is often far less sharp than 

 in other vascular plants, 1 we need feel no great scruple 

 in applying the terms roots and rootlets to the 

 Stigmarian organs, as was constantly done by William- 

 son, their chief investigator. Some further suggestions 

 will be considered in Chapter XIV. 



III. LYCOPODITEAE 



Under this name are included certain fossil Lyco- 

 pods, occurring from the Devonian onwards, which 



1 On this subject see C. E. Jones, " Morphology and Anatomy of the 

 Stem of the Genus Lycopodium" Trans. Linn. Soc. ser. ii. vol. vii. 1905 ; 

 G. Wigglesworth, "Young Sporophytes of Lycopodium complanatum and 

 L. clccvatum," Ann. of Bot. vol. xxi. 1907. 



