EMBRYOLOGY 



34i 



exposed freely above ground, and is of a green colour : in L. cernuum 

 and inundatum it bears numerous irregular leaf-like lobes, though in 

 L. salakense the lobes are rudimentary or absent (Fig. 178). The pro- 

 thallus is evidently in the main a self-nourishing body, though an endo- 

 phytic fungus is almost constantly present, indicating a second but 

 subsidiary line of saprophytic nutrition. As the prothallus grows a 

 merismatic zone is localised surrounding the upper part of the cylindrical 

 body, but below its apex : this contributes to increase both the upper and 



FIG. 178. 



Young leafy plant of Lycopodhtm ccrnuntu, L., with the prothallus, bearing its irregular 

 assimilating lobes, attached on its left-hand side. X about 20. fAfter Treub.) 



lower regions, while above it the green expanded lobes are formed. The 

 sexual organs appear between the latter, the youngest being nearest to the 

 merismatic zone. 



A second type shows in the ascendant that method of nutrition which 

 was subsidiary in the first : it is exemplified by the large subterranean 

 prothalli of L. complanatum, clavatum, and annotinum: being shut off from 

 light these prothalli are colourless, and the leaf-like lobes are absent. The 

 massive prothallus is composed of a lower region which takes a conical 

 form, the angle of the cone being greater in L. clavatum and annotinum 

 than in L. coniplanatum : it is in this region, as in /. cernuum, that the 

 endophytic fungus is present. The merismatic zone is active as before at 

 its upper limit, and above it is the part which bears the sexual organs, 

 but without any vegetative lobes as in L. cernuum (Fig. 1791:). It is clear 



