Schwarze: Cleavage in Sporangia 155 



eral points, but recent students have in a number of cases failed 

 to take account of the evidence he has presented as to the con- 

 traction and expansion phases accompanying cleavage. I have 

 studied Achlya and Saprolegnia in both living, sectioned, and 

 stained material, and my observations confirm those of Rothert. 



The process of cleavage is similar to that I have already de- 

 scribed for Olpidiopsis saprolegniae. The cleavage is progressive, 

 the furrows appear first on the inner surface of the parietal proto- 

 plasmic layer and give the latter an undulated appearance. Grad- 

 ually these clefts become sharper and reach the plasma membrane. 

 In optical view these protoplasmic masses resemble the old-fash- 

 ioned sugar-loaves. Viewed from the surface the protoplasmic 

 masses are roughly polygonal. The spore initials are generally 

 described as being connected by fine protoplasmic strands. I am 

 inclined to interpret these strands as gelatinous exudates of the 

 spore initials. Rothert described the development of spores in 

 very slender sporangia as a heaping of protoplasm on the proto- 

 plasmic membrane. It is a question whether there is much, if any, 

 increase in the radial diameter of the protoplasmic layer on the 

 median axis of the spore initials. A better interpretation of the 

 spore formation in these sporangia and in the oogonia is to regard 

 it as a process of cleavage, the furrows bemg at first broad and 

 shallow instead of sharp and deep. 



The spore initials now contract and the clefts become prominent. 

 The protoplasmic masses now become densely granular, are highly 

 refractive, and assume more definite outlines. This stage is 

 quickly followed by a splitting of the protoplasmic membrane 

 which is drawn in by the isolated spore initials as they round up. 

 Division of the protoplasmic content is now complete, each defini- 

 tive spore is uninucleated and is homologous with the uninucleated 

 protospores Harper described in Synchytrium decipiens. 



As first noted by Rothert and confirmed by Harper, the splitting 

 of the elastically stretched plasma membrane is attended with a 

 marked shrinkage of the sporangium wall accompanied by the ex- 

 pulsion of part of the cell-sap through the sporangial wall. The 

 basal septum, which has heretofore been concave, is now pushed 

 up by turgor into the sporangium and assumes a convex configura- 



