Schwarze: Cleavage in Sporangia 



161 



MUCOR RACEMOSUS 



Apparently no one since Leger (34) has studied spore formation 

 in Mucor racemosus. Leger claims for it, as for all sporangia, 

 that the spores are cut out simultaneously as polyhedric blocks. 



Moreau (37) has studied Mucor spmescens and he describes 

 vacuolization of the protoplasm resulting in long strands, which 

 become nodular and then break up into uninucleate or several 

 nucleated spores. He gives no further account of the process. 



I have studied Mucor racemosus relative to the process of spore 

 formation. I find that spore formation is initiated by furrows, 

 which start as the periphery of the spore plasm and cut out multi- 

 nucleated blocks of irregular size (PI. 16, fig. 16). Further fur- 

 rowing cuts up these blocks into irregular protoplasmic masses 

 containing a few nuclei. These protoplasmic masses then grow 

 and become polyhedral. This expansion stage is followed by a 

 second contraction, the spores round up and develop a cell- wall. 

 The mature spores may contain seven to eight nuclei. I have not 

 observed a protospore stage. The process of spore formation, as 

 in Sporodinia grandis, is abbreviated, but the spores have thicker 

 walls and are viable for a longer period. They are also more 

 uniform in size than those of Sporodinia grandis. 



ClRCINELLA MINOR 



Moreau (37), studying spore formation in Circinclla conica, 

 states that the center of the sporangium is at times occupied by a 

 large vacuole. The formation of spores is accomplished by irregu- 

 lar vacuoles, which cut up the spore plasm into amoeba-like bodies 

 bound together by protoplasmic strands. These strands become 

 thinner and break, the protoplasm then contracts about each nu- 

 cleus, rarely around two. Moreau compares these protoplasmic 

 bodies to the protospores Harper described in Pilobolus crystal- 

 linus. The nucleus then divides and each protoplasmic mass be- 

 comes multinucleated, the spores become polygonal and press 

 against one another. At maturity they become globular and 

 smooth. 



I have studied spore formation in Circinella YYiinor, but my ob- 

 servations do not agree entirely with those of Moreau. Cleavage, 



