220 AQUATIC PHYCOMYCETES 



ogy, and biology of the species. He noted that over 90 per cent of the 

 colonies collected from the pond over a period of ten days were in- 

 fected by the fungus. The least infected had from one to two chytrids 

 on them, the most, from seventeen to eighteen. Sterility of the colony 

 resulted from heavy infections of the germinocysts. Coenobia bearing 

 numerous chytrid invaders soon dropped to the bottom of the pond 

 and disintegrated. 



Concerning the development of the thallus Hovasse observed that 

 the zoospore appears to attack the moving colony, attaching itself 

 on the surface at the point where the flagella emerge. A slender tube 

 is produced from the spore body and passes through the flagellar 

 canal and into the cell contents, expanding distally to form the spherical 

 haustorium. The more proximal portion of the tube and eventually 

 the body of the zoospore itself expand and form the sporangium. The 

 young sporangium is at first terminated by a beaklike process, the 

 body of the zoospore, which disappears later; at maturity the tip of 

 the sporangium is broad. Both Gimesi and Hovasse noted that the 

 young thallus is binucleate. 



Hovasse's preparations showed that the single nucleus of the spore 

 migrated from the spore body into the expanding rudiment of the spo- 

 rangium. There it enlarged and divided, although actual mitotic fig- 

 ures were not observed. The subsequent divisions of the daughter 

 nuclei were not exactly synchronous, one nucleus, for example, being 

 in late anaphase while the other was only in the metaphase. Division 

 was intranuclear, and a centrosome was present at either pole of the 

 spindle. In later stages enlargement of the nuclei occurred, followed 

 by a simultaneous division which reduced their size and changed their 

 configuration. Division of the cytoplasm was preceded by the appear- 

 ance of large osmophilic vacuoles at one pole of each of the nuclei. 

 Actual cytoplasmic division then progressed rapidly to all parts of 

 the sporangium and separated the polygonal elements, each of which 

 surrounded a nucleus. These segments became the zoospores. 



Phlyctidium bumilleriae Couch 

 J. Elisha Mitchell Sci. Soc. 47: 256, pi. 17, figs. 66-68. 1932 

 "Sporangia sessile, globose, 5.4-7.6 u. thick, with a small bulbous 



