262 



STRUCTURE AND LIFE HISTORIES 



spores of ferns, mosses, liverworts, and algae by usually, if 

 not always, possessing more than one nucleus. They 

 secrete a slimy substance in which they are imbedded. 



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.) 



When ripe the wall of the sporangium bursts open (Fig. 

 i8q), and the spores, thus set free, float away through the 

 air in countless millions. So widely and so thickly are 



