262 
STRUCTURE AND LIFE HISTORIES 
asexual spores, but differ from the spores of ferns, mosses, 
liverworts, and algae by usually, if not always, possessing 
more than one nucleus. They secrete a slimy substance 
FIG. 1 88. Rhizopus nigricans. i, Section of sporangium, showing 
cleavage of peripheral cytoplasm much further advanced than in Fig. 187. 
Furrows are here cutting outward from the columella cleft, X about 200; 
2, section of sporangium in which the spores are completely formed, 
rounded up, and surrounded by thin walls. The columella wall is also 
formed, X about 200; 3, ripe spores in their living condition, showing 
variations in size, and ridges on their walls, X over 350. (After D. B. 
Swingle.) (Cf. Figs. 186 and 187.) 
in which they are imbedded. When ripe the wall of 
the sporangium bursts open (Fig. 189), and the spores, 
thus set free, float away through the air in countless 
