158 



Mycologia 



spore origins are definitely formed, and that, though fused into a 

 mass in which individual spores can not be made out, yet each 

 nucleus has obtained a hold on a certain mass of cytoplasm. . . .." 



The sudden appearance of the polygonal spore masses at the 

 beginning of the second contraction phase has given rise to such 

 theories as the simultaneous cleavage of the sporangial protoplasm 

 into polygonal masses and the cutting out of the spores by cell- 

 plates. I have already summarized these views and I need not 

 repeat them here. 



The polygonal spores of Saprolegnia undergo a further contrac- 

 tion and subsequently round up. The turgor in the sporangium is 

 decreased to such an extent that the basal wall now becomes convex 

 inward. At this stage the sporangium decreased still more in 

 length. Thus during the period of greatest turgidity the sporan- 

 gium measured 94 microns in length. When the spores were fully 

 matured the sporangium had contracted eight microns in length 

 and six microns in width. 



The observations of Rothert (46) relative to the escape of the 

 cell-sap and the concomitant shrinking of the sporangium during 

 spore formation in Saprolegnia, Harper's evidence of similar phe- 

 nomena in Synchytrium decipiens, Kusano's observation of shrink- 

 age in Synchytrium puerariae, Swingle's account of progressive 

 cleavage in Rhizopus nigricans and Phycomyces nitens, Harper's 

 studies of spore formation in the sporangia of Sporodinia grandis 

 and Pilobolus, Butler's observations relative to shrinkage in the 

 sporangia of Pythium intermedium and Pseudolpidium aphano- 

 mycis, Harper's and Dodge's observations of the extrusion of 

 water into vacuoles during the early stages of the formation of 

 sporangia in Trichia, as well as my own observations, lead me to 

 corroborate the contention of Harper that the exudation of water 

 is a factor in the process of segmentation of the protoplasm. Har- 

 per compares the furrowing of the spore plasm with the cracking 

 of a drying, colloidal mass. The fact that vacuoles or furrows 

 never cut out protoplasmic segments devoid of nuclei is proof that 

 the latter are the centers which control the water loss and thus the 

 cleavage process. This may be explained by assuming that the 

 nucleic acids manifest an attraction or affinity for water greater 



