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AQUATIC PHYCOMYCETES 



Fig. 9. Cytology of Polychytrium aggregation Ajello 

 A. Early stage in the germination of a zoospore. B. Young thallus 

 with persistent zoospore cyst and broad branched germ tube. C. Late pro- 

 phase stage of nucleus in zoospore cyst. D. Metaphase of germinating 

 zoospore nucleus, with thickened wall of zoospore cyst. E. Metaphases 

 in second nuclear division in a young thallus. F. Multinucleate young 

 thallus showing nonsynchronous nuclear division. G. Metaphase of the 

 primary nucleus in a young sporangium. H. Binucleate zoosporangium. 

 /. Anaphases of second nuclear division. /. Trinucleate sporangium 

 with metaphase nuclei, one metaphase plate in polar view. K. Early pro- 

 phase nucleus showing ill-defined densely stained reticulum shrunken to- 

 gether and crescent-shaped nucleolus. L. Late prophase stage showing 

 formation of chromosomes. M. Very late prophase stage with chromosomes 

 approaching the equator of the spindle. N. Metaphase nucleus with five 

 or six chromosomes forming a band on equator of spindle. O. Meta- 

 phase plate (polar view) showing chromosomes arranged in a ring and lateral 

 nucleolus close to nuclear membrane. P. Anaphase stage with elongated 



