350 LYCOPODIALES 
sunken in the soil. The embryo is long dependent for nourishment entirely’ 
upon the large prothallus; hence its swollen haustorial foot, which s de- 
veloped most strongly in the direction of the largest nutritive supply, reacting 
meanwhile upon the disposition of the other parts of the embryo: in point of 
origin this is the consequence of unequal turgid distension and division 
of cells of the foot-tier, which in the Se/ago-ttype remain small. The first 
Fic. 187. 
Lycopodium cernuum. Young embryo emerging from the prothallus. @z=neck of 
archegonium ; s=suspensor ; I.-I. basal wall, corresponding to 4, 6 in Fig. 182, to II.-II. 
in Fig. 185, and to IV.-IV. in Figs. 183 and 186; cof=cotyledon; z¢ub=tubercle of 
protocorm. x 300. (After Treub.) 
leaves—here an opposite pair, though in other species there is a single 
cotyledon—are only scale-leaves, which may serve for protection of the 
apex in forcing its way upwards through the soil; but this is only a 
derivative function, and it can hardly be doubted, after comparison with 
the embryo of Z. Seago, that the foliage character of the first leaves was 
the prototype, and that the early formation of colourless scale-leaves in the 
clavatum-annotinum-type is a concomitant of the subterranean habit adopted 
by their prothalli. 
tee. 
