350 



LYCOPODIALES 



sunken in the soil. The embryo is long dependent for nourishment entirely 

 upon the large prothallus ; hence its swollen haustorial foot, which is 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-type remain small. The first 



FIG. 187. 



Lycopodium cernuum. Young embryo emerging from the prothallus. a?- = neck of 

 archegonium ; s = suspensor ; I. -I. basal wall, corresponding to b, b in Fig. 182, to II. -II. 

 in Fig. 185, and to IV.-IV. in Figs. 183 and 186 ; cot- cotyledon ; tub - 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 L. Selago, that the foliage character of the first leaves was 

 the prototype, and that the early formation of colourless scale-leaves in the 

 davatum-annotinum-\y\& is a concomitant of the subterranean habit adopted 

 by their prothalli. 



