Schwarze: Cleavage in Sporangia 159 



than that displayed by the cytoplasm; hence, as Harper has sug- 

 gested, the loss of water may be least in the vicinity of the nuclei. 



Sporodinia grandis 



Spore formation in the sporangia of Sporodinia grandis was 

 regarded by both Van Tieghem (55) and Leger (34) as a con- 

 densation of the spore plasm into polyhedric masses, which later 

 round up. Harper (24) has figured a number of stages in spore 

 and columella formation. Swingle (50), a few years later, studied 

 the same fungus and reports that his results are entirely in accord 

 with those of Harper. 



As Sporodinia represents an extreme type as to the speed of 

 spore formation, I have studied the process further in the light of 

 the conceptions of contraction and expansion first developed by 

 Rothert from his studies on the sporangia of Saprolegnia. I find 

 the dome formed by series of large vacuoles, which flatten, fuse, 

 end to end, and separate the spore plasm from the columella plasm 

 as described by Harper. I have, however, a number of slides (PI. 

 15, figs. 1, 6) which show an interesting variation of the process in 

 that the vacuoles are completely fused on one side of the sporan- 

 gium, while on the other side they are either somewhat globose or 

 flattened. Swingle's fig. 8, plate 2, shows that in Rhizopus nigri- 

 cans the columella formation may be more advanced on one side of 

 the sporangium. A few times I observed surface furrows cutting 

 in at the base of the sporangium, to meet the flattened vacuoles, 

 which cut out the columella (PL 15, fig. 6). Harper has described 

 a similar phenomenon in Pilobolus and Swingle in Rhizopus 

 nigricans. 



In Sporodinia spore formation may begin before the columella 

 cleft is complete. Swingle notes that this often occurs in Rhizopus 

 nigricans (see his fig. 8, plate 2). This shows, it seems to me, 

 that the columella formation and cleavage are two parts of one 

 general contraction phase. The cleavage is progressive and may 

 begin by the formation of furrows at the surface or at the colu- 

 mella cleft (PI. 15, figs. 1, 2). It is to be noted that cleavage is 

 more advanced in that region where the fusion of vacuoles has 

 produced the columella cleft (PI. 15, fig. 6). The furrows cut 



