REPRODUCTION OF LYCOPODIUM 



315 



The sporophylls (Fig. 179, B) are similar to the foliage-leaves, 

 and are commonly in whorls ; they are readily recognised by the 

 single large, somewhat kidney-shaped, sporangium which each 

 bears on its upper surface. In most species the sporophylls are 

 aggregated in cones, as in Equisetum, although in L. selago, for ex- 

 ample, the reproductive region is not clearly marked, zones of sporo- 

 phylls usually alternating with 

 vegetative leaves. Another pecu- 

 liarity of this species is the 

 development of large bulbils in the 

 axils of the uppermost leaves ; 

 these structures, which serve for 

 vegetative reproduction, must 

 not be mistaken for fertile 

 leaves. 



The cones, when present, oc- 

 cupy the ends of erect branches, 

 which are of the ordinary type, ex- 

 cept in L. davatum (Fig. 179, 'A) ; 

 here they bear minute leaves, 

 at rather wide intervals, con- 

 trastingmarkedly with the densely 

 arranged sporophylls of the cone. 

 Each sporangium contains nu- 

 merous spores (Fig. 179, D) 

 which, after being shed, give 

 rise to peculiar fleshy prolhalli 

 (Fig. 179, C). In most species 

 these grow underground as sapro- 

 phytes, obtaining their food with 

 the aid of a mycorrhiza from 

 the humus in which they are 



embedded. Both kinds of sexual organs are borne on the same 

 prothallus. 



Although Selaginella is represented in Britain only by 

 5. spinosa (Fig. 180, C), which is found in similar habitats 

 to those frequented by our species of Lycopodium, several 

 members of the genus are commonly cultivated in greenhouses. 

 The general habit is like that of Lycopodium, but in most 



FIG. 178. The Quillwort (Isoetes 

 lacustris), somewhat reduced. 



