LIXNEAN SOCIETY OF LOXDOX. 



75 



the Lycopodiales we are not limited to the two alternatives root 

 or stem, since Goebel and Bruchmann have shown that the 

 rhizophores of Sdaginella are indeterminate organs which can 

 develop either as root-bearers or as leafy shoots. Their position 

 in the young sporophyte of Selaginella is very suggestive of 

 analogy with the Stigmarian axes, and attention has been drawn 

 to this by Scott, Bower, and others. But the peculiarly root-like 

 structure of these rhizophores and the fact that they produce 

 their roots endogenously, shows that they are in Selaginella very 

 highly specialised. The Stigmarian axes though undoubtedly 

 analogous structures are more stem-like in their character and 

 probably more primitive. A more useful comparison might 

 therefore be made between Stigmaria and the very primitive 

 Phylloglossiim. 



Here we have not only exogenous and adventitious roots 

 developed at the base of the leaves (cf. Sigillaria spinidosa), but 

 in similar positions one or more outgrowths are produced which 

 serve the purpose of vegetative reproduction. But though 

 specialised for this function, they are, I believe, of the same 

 indeterminate natui'e as the rhizophores of Selaginella ; and as 

 they show more resemblance to true shoots and bear their roots 

 exogenously, they are really more closely analogous to the 

 Stigmarian axis. Organs of this nature would probably have 

 bifurcated in the case of the extinct Lycopodiales, to keep pace 

 with the physiological requirements of the branching main axis. 

 They may possibly possess the power of forming under certain 

 conditions upright leafy stems, which would explain some structures 

 figured and described by G-rand'Eury and others. 



The conformation of the underground axes of Stigmariojms 

 and the still more pronounced contraction of the base of 

 Pleuromeia and of Isoetes, would be explained by reduction of 

 the requirements of the plants so far as root-absorption was 

 concerned. 



