156 



Mycologia 



tion. Rothert estimated the shrinkage at 13 per cent. Butler (9) 

 finds that at a corresponding stage the diameter of the sporangium 

 of Pythium intermedium decreased by about one tenth. The same 

 author also noted a contraction of the sporangium of Pseudolpid- 

 ium aphanomycis immediately after the disappearance of the large 

 central vacuole. Harper called attention to the fact that in Syn- 

 chytrium decipiens the cleavage was accompanied by pronounced 

 shrinkage. He found that when cleavage was complete the total 

 volume of the segments had been reduced to such an extent as not 

 to occupy more than approximately one third of the volume of the 

 primordial cell. Kusano also reports a shrinkage of the segments 

 in the sporangia of Synchytrium puerariae during the cleavage 

 process. 



Fig. B. Saprolegnia torulosa: 1, tip of hypha which will become a sporan- 

 gium; 2-7, show varying appearances of the central vacuole; 7, first appear- 

 ance of cleavage, furrows irregular and not corresponding to the definitive 

 furrows ; 8-9, spore masses outlined by rather shallow furrows, the two oval 

 outlines in these figures, and also in figures 10, represent the end views of 

 spore initials projecting up from below; 10, clefts have become deeper; if, 

 spores have become polygonal through mutual pressure ; this stage soon follows 

 the rupture of the plasma membrane and represents an expansion phase of the 

 spores ; the basal wall is now convex toward the sporangium showing that its 

 plasma membrane is ruptured. 



