SAPROLEGNIALES 



821 



known. Magnus (1872: 87) stated that he observed in one instance that 

 the zoospore came to rest on the wall of the alga, penetrated it, and pass- 

 ed into the contents. Sparrow, on the other hand, presented evidence 

 that the zoospore encysts on the surface and then produces a penetration 



Fig. 62. Eurychasmidium tumefaciens (Magnus) Sparrow in Ceramium 



diaphanum 



A-B. Early stages in formation of thallus ; host cells are beginning to hyper- 

 trophy. C. More mature thallus, showing at bottom of left-hand side the 

 remains of infecting zoospore and its penetration tube. D-F. Strongly hyper- 

 trophied host cells with vacuolate thalli of fungus in them. G. Empty spo- 

 rangium showing the many discharge tubes and a few of the discharged, encyst- 

 ed, zoospores ; latter are so numerous as to form a dense cloud around infected 

 region. H. Angular cysts produced by discharged zoospores, from all but one 

 of which spores have emerged. 



(Sparrow, 1936b) 



