344 



LYCOPODIALES 



In considering these various prothalli it is then clear that they are 

 all modifications of the same conical form : that the several parts, though 

 differing in proportion, have the same positions relative to one another 

 and to the sexual organs which they bear, while the differences are closely 

 related to the differences of circumstance and of nutrition. There is 

 reason to believe that the full chlorophyll-nutrition was the primitive state 

 for them ail, and the saprophytic nutrition, seen in the subterranean or 



the epiphytic types, a deriva- 

 tive state. On this basis the 

 certiitum-type would be recog- 

 nised as relatively primitive, 

 while Z. Selago, being less 

 specialised than the annotinnm 

 or fiMegmaria-types, would 

 approach it more nearly than 

 they do. But it does not 

 follow necessarily that a species 

 which is recognised as primi 

 tive in respect of one prominent 

 feature, is to be held as primi- 

 tive in all its features. This 

 applies to Z. cernuum : it is 

 true that its prothallus is green 

 and assimilating, and in this 

 respect probably primitive; but 

 its sporophyte is a fairly 

 advanced one, with definite 

 strobili, and with peltate chaffy 

 sporophylls strongly differen- 

 tiated from the assimilating 

 leaves : its axis, too, shows 

 an advanced condition of the 

 stele. Thus in its general 

 characters Z. cennntm cannot 

 be held as a consistent proto- 

 type of the genus. But, on 



the other hand, Z. Selago has a prothallus little removed from the condition 

 seen in Z. cernuum, while in addition the sporophyte of that species has 

 been seen to represent the least differentiated type in the whole genus. 

 On the general sum of its characters it would accordingly take a place as 

 a relatively primitive form. But its prothallus shows distinct plasticity in 

 the directions along which specialisation has extended to produce the 

 more extreme types : on the one hand, its subterranean specimens, with 

 elongated cylindrical form, prefigure the more specialised developments of 

 Z. com f> la natum and annotinum : the compressed and flattened form 



/%! xm- 



FIG. 181. 



Median longitudinal section through a young prothallus of 

 LycopotHiini Selago. ^ = basal cell; nh, root hairs; ^ = epi- 

 dermis ; r=the investing tissue, stored with reserve materials, 

 and harbouring an endophyte ; r = the central ; ^ = the genera- 

 tive tissue; ;-=archegonium ; X- = young embryo ; # = anthe- 

 ridia beginning to develop: ^// = sexual hairs. X 35. (After 

 Bruchmann.) 



