Schwarze: Cleavage in Sporangia 163 



Pilobolus crystalUnus and Synchytrium decipiens. It is evident 

 that the process of spore formation in Circinella minor, like Rhizo- 

 pus nigricans, occupies an intermediate position in such a series. 

 In Circinella minor the formation of. protospores is followed by 

 nuclear division and growth. But with the formation of the proto- 

 spores cell-division is complete. In Pilobolus crystalUnus the 

 protospore grows and becomes multinucleated, but this multi- 

 nucleated cell divides by constriction. The final cell-divisions pro- 

 duce the oblong, binucleate spores. In Sporodmia grandis the 

 process of spore formation is so abbreviated that the initial cleav- 

 age cuts out comparatively large multinucleated segments which 

 ultimately round up and become the definitive spores. 



I have illustrated the chief stages of the development of the 

 columella and spores in Mucor mucedo in a series of text figures 

 (text fig. D, 1-5). 



Fig. D. Diagrams showing the method of the columella and spore forma- 

 tion in Mucor mucedo. i, a young sporangium. 2, showing the dome-shaped 

 layer of vacuoles outlining the columella. 3, showing the spore plasm cut up 

 into protoplasmic blocks by progressive cleavage. 4, spore-initials in the con- 

 traction stage. 5, showing the polyhedral or expansion stage. 



MUCOR MUCEDO 



Strasburger (49) has given us a fragmentary account of spore 

 formation in Mucor mucedo. He considered the protoplasmic 

 mass cut up by cell-plates in a manner similar to that in Sapro- 

 legnia. Two years later Biisgen (8), studying the same species, 

 came to the conclusion that the spore plasm is cut up into large 

 protoplasmic blocks by cell-plates, and that by subsequent sub- 

 division protoplasmic masses are formed which have the size of the 

 definitive spores. The sporangium then becomes homogeneous 

 and a second division produces the definitive spores. Leger (34) 

 studied spore formation in the sporangia of Mucor mucedo and 



