154 



Mycologia 



almost obliterated. Nor can I agree with Butler, who describes 

 the formation of " protoplasmic heapings " and the delimitation of 

 multinucleated, protoplasmic masses, which are later cut up by 

 cleavage furrows, to form the spore origins. In no case did I 

 observe any fusion of spore initials and the resulting production 

 of a homogeneous state such as Butler describes for Pseudolpidium 

 aphanomycis and as was held by Strasburger and Biisgen to occur 

 in Saprolegnia. 



We can summarize, roughly, the following stages in the spore 

 formation of Olpidiopsis saprolegniae Cornu : 



1. Protoplasm with many small vacuoles, 



2. The formation of large vacuoles more or less centrally disposed and the 



concomitant production of an exit-tube. 



3. The coalescence of large vacuoles into a large central vacuole. 



4. Progressive cleavage by furrows cutting outward from the central vacuole. 



(First contraction phase.) 



5. Cleavage of plasma membrane, shrinkage of the sporangium and disappear- 



ance of the central vacuole. 



6. Swelling of the spore initials to the polygonal closely pressed areas com- 



monly observed. 



7. Second contraction phase — appearance of hyaline spaces between spore ini- 



tials (often erroneously interpreted as cell plates). 



8. Further contraction leading to the rounding up of the spore masses and 



their swarming movements. 



The above conclusions were reached after carefully studying the 

 cleavage phenomena in dozens of sporangia in hanging-drop cul- 

 tures. 



Saprolegnia and Achlya 

 Rothert (46) recognized three types of sporangia in the Sapro- 

 legniaceae : " gef iillte Sporangien," those completely filled with 

 protoplasm ; " inhaltsarme," those having a thin parietal layer of 

 protoplasm ; and " normale," sporangia with a thick parietal layer, 

 the predominant form. Rothert figured furrows cutting through 

 the protoplasm from the central vacuole outward and notes that 

 these furrows appear practically simultaneously throughout the 

 whole length of the sporangium. Rothert's observations on spore 

 formation in Saprolegnia and Achlya are of great importance for 

 understanding the cleavage phenomena in the other sporangia. 

 Harper has reviewed and confirmed Rothert's observations in sev- 



