Schwarze: Cleavage in Sporangia 



153 



evident (text fig. A, 6, 7), and after the elapse of one minute they 

 cut through the latter and the large vacuole disappeared. Cleavage 

 is now complete and here and there the outlines of the spores can 

 be made out (text fig. A, 8). After two minutes the protoplasm 

 became very granular and the hazy outlines of polygonal spore 

 masses were recognizable. I can only interpret this polygonal 

 stage as due to rapid growth of the spore initials, which thus press 

 against one another and become polyhedral. One minute after 

 the appearance of the compact, polygonal spore initials a contrac- 

 tion occurred, the inter-sporal substance appearing as hyaline lines. 



Fig. A. Olpidiopsis saprolegniae : 1-2, median view of sporangia showing 

 several rounded vacuoles; 3, sporangium showing coalescence of the vacuoles; 

 4-8, different series than 1-3 in which the wall layer is thinner; 4-5, sporangia 

 showing vacuoles of various shapes ; 6-7, sporangia showing early cleavage 

 stages ; 8, sporangium showing apparent homogeneous stage following the 

 rupture of the plasma membrane; 9-10, another individual, sporangia show 

 radial furrows; 10, cleavage has occurred in the exit tube. 1-2 and 4-10 

 show exit tubes. 



One minute later the spores underwent a further contraction ; they 

 rounded up and almost immediately began to move to and fro. 

 Within two minutes the zoospores escaped through the exit tube. 

 Thus within eighteen minutes of the first formation of a cleavage 

 furrow the spores formed and escaped. If one considers the 

 rapidity of these changes, one can readily infer why the cleavage 

 furrows, extending outward from a central vacuole, are so seldom 

 seen in fixed sections. I can not agree, therefore, with Barrett 

 that the spore formation occurs simultaneously. I would interpret 

 his figure 39 as a contraction stage following the so-called homo- 

 geneous state, of Strasburger and Biisgen, in which the spore 

 initials are so closely pressed together that their boundaries are 



