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. 188. — 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 sporangmm bursts open (Fig. 189), and the spores, 

 thus set free, float away through the air in countless 



