EMBRYOLOGY 



341 



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

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

 Z. 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 



. r 



FIG. 178. 



Young leafy plant of Lycopodium cernuum, L., with the prothallus, bearing its irregular 

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



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

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

 icrismatic 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 

 )thalli of L. complanatum, davatum, and annotinum\ being shut off from 

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

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

 >rm, the angle of the cone being greater in Z. davatum and annotinum 

 than in Z. complanatum: it is in this region,, as in Z. cernuum, that the 

 idophytic 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, 

 >ut without any vegetative lobes as in Z. cermium (Fig. 179 B). It is clear 



