296 



LYCOPODIALES 



approaches L, Selago in its alternation of successive sterile and fertile 

 zones. On such grounds the innndafam group has been associated with 

 Phlegmaria by Baker in the sub-genus Lepidotis, though this association 



is not now upheld. In the rest, however, the 

 definition is more exact, and is strictly main- 

 tained ; for instance, in L. cernuum in a very 

 large number of specimens a transition from 

 the strobilus back to the vegetative shoot was 

 never observed. The same is the case in the 

 species associated as the group of L. clavatum, 

 which are terrestrial trailing species, with well- 

 defined strobili. In this series the intercalation 

 of a peduncle, with small distant scales, between 

 the larger-leaved foliage shoot and the definite 

 strobilus is indicated (Fig. 144). The question 

 whether the peduncle is directly derived from the 

 basal part of the strobilus, or from a specialised 

 part of the already sterile foliage region, may be 

 left open ; but as sporangia are not found on it, 

 nor even any vestiges of arrested sporangia, the 

 latter seems the more probable source of the 

 peduncle : the biological importance of it in 

 ground-growing forms is readily understood. 



Finally, the dorsiventral species, previously 

 grouped as the sub-genus Diphasium, are now 

 distributed according to their obvious affinities; 

 the dorsiventral character of their vegetative 

 shoot being held as a secondary adaptation : 

 the strobilus, however, remains as clearly defined 

 as in the more advanced representatives of the 

 sub-genus Rhopalostachya, and does not share in 

 the dorsiventral development. 



A comparison of the living species of Lyco- 

 podium thus appears to demonstrate a progression 

 from a less differentiated to a more differentiated 

 state. In the simplest forms the whole of the 

 unbranched or sparsely-branched shoot is practi- 

 cally a fertile strobilus, which serves the double 

 purpose of assimilation and of spore-production. 



By gradual steps the living species suggest how the two functions became 

 separated : a purely vegetative region was established by abortion of the 

 sporangia, and it was naturally located in the first-developed or lower part 

 of the plant, since the function of nutrition must necessarily precede that 

 of spore-production. The fertile upper region also became more specialised, 

 and in the species where it is most clearly defined from the vegetative region 



FIG. 144. 



Lycopodium carolinianutn, L. 

 .<4=figure showing habit. About 

 two-thirds natural size. B stro- 

 bilus. Natural size. C = sporophyll 

 seen from above. x6. Z> = the 

 same from the side. x6. (After 

 Engler and Prantl.) 



