SPORE-PRODUCING MEMBERS 



315 



assist in conveyance of nourishment to the large mass of developing 

 spores. Thus in the main features of form and dehiscence the sporangia 

 of Rhopalostachya conform to the type of Z. Selago, but are larger and 

 more productive; while the sporophylls have a more elaborate form for 

 purposes of protection. This goes along with the differentiation of the 

 vegetative from the propagative regions, the steps of which have been 

 traced above in the genus Lycopodinm. The conclusion seems justly to 

 follow that with this differentiation, which has apparently involved a 

 diminution in the actual number of sporangia by abortion, there has come 



FIG. 161. 



Lycoppdium alpinutn, L. A Radial section through a sporophyll and young 

 sporangium. .5 = the same older; in both the sporogenous tissue is shaded. D radial 

 section of an older sporangium ; s/ = stem. C= tangential section of a sporangium of Lye. 

 clavatum, of similar age to D ; in both these figures the sporogenous tissue is referable 

 in origin to three rows of cells. A, fi, Cx 200. D X 100. 



into existence a more massive type of sporangium, together with a more 

 extensive spore-output from each of them, and a more specialised protec- 

 tion of them while young. 



It has been seen that the strobilus of Phylloglossum resembles that of 

 the sub-genus Urostachya^ rather than that of Rhopalostachya. An exami- 

 nation of the developing sporangium supports this comparison, for only a 

 single row of about six archesporial cells is found; but, on the other 

 hand, the outline of the sporangium, and the relative thickness of the 

 stalk, show some similarity to Z. immdatum. 



The sporangium of Selaginella corresponds in general type to that of 

 Lycopodium. It is usually described as arising from the surface of the 

 axis: in some species it does so (S. Martensii) (Fig. 162), but in others 

 it is seated more nearly upon the surface of the leaf; in fact its position 



