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Fig. 93. Development of the .sporangium of Rhizopus nigricans. A, young sporangium; 

 B, appearance of small vacuoles between outer and inner parts of sporangium; C, enlarge- 

 ment and fusion of vacuoles to form columella cleft; appearance of cleavage furrows at 

 outer surface; D, enlarged view, showing early cleavage furrows and scattered nuclei and 

 vacuoles; E, sporangium completely cut off from columella; cleavage further advanced; F, 

 mature sporangium. (After Swingle.) 



