912 AQUATIC PHYCOMYCETES 



rett's cytological preparations of sporangia in the resting, vacuolate, 

 condition showed very definitely, however, that in his material the spore 

 centers were already formed and that some fragmentation had been 

 initiated. He considers the heaping described by Butler simply a 

 phenomenon accompanying final stages in the maturation of the spores. 

 According to Barrett, the zoospores are produced simultaneously by 

 division of the protoplasm, and upon the gelatinization and dissolution 

 of the tip of the discharge tube the swarmers emerge from the spo- 

 rangium as vacuolated uninucleate biflagellate structures. Schwartze 

 (1922), on the other hand, from observations only of living material of 

 O. saprolegniae, described the cleavage as progressing rapidly outward 

 from a central vacuole. When the furrows pierced the thin peripheral 

 layer of cytoplasm the vacuole vanished and the outline of the zoospores 

 became distinguishable. Subsequent development involved the appear- 

 ance of definite polygonal segments followed by contraction of the 

 whole mass. A further contraction resulted in the rounding off and 

 rocking of the individual spores, which escaped after two minutes. This 

 report agrees, in the main, with the classic account of Rothert (1888) of 

 cleavage in Saprolegnia and with the observations of McLarty (1941a, 

 1941b) on Olpidiopsis. 



The zoospores of Olpidiopsis are relatively small and numerous. The 

 body, in general, is somewhat ovoid, or reniform with a narrower 

 anterior end. The contents are rather granular. From the forward end 

 two oppositely directed flagella of approximately the same length 

 emerge (Fig. 73 A, p. 906). 



In the primarily marine Peter senia the thallus may extend through 

 one or more cells (Fig. 76 D, p. 960). Its contents are refractive and 

 bear numerous large spherical vacuoles. A homogeneous condition 

 ensues, which is followed by the cleavage of the zoospores. This process 

 has not been observed in its initial phases. The zoospores in their later 

 stages of maturation within the sporangium undergo a rocking and 

 twisting movement very much like that found in Pythium. They are 

 minute, grape-seed-like, and laterally biflagellate (Fig. 76 H) (Sparrow, 

 1934c). 



As yet there are not available any precise details concerning the 

 sequence of protoplasmic changes in the developing sporangia of 



