EMBRYOLOGY 341 
exposed freely above ground, and is of a green colour: in Z. cernuum 
and ¢nundatum 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 
Fic. 178. 
Young leafy plant of Lycopodium cernuuim, L., with the prothallus, bearing its irregular 
assimilating lobes, attached on its left-hand side. X about 20. (After 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 Z. 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 Z. clavatum and annotinum 
than in LZ. complanatum: it is in this region, as in ZL. 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 Z. cernuum (Fig. 179 B). It is clear 
