1920] WILSON— CROWN -GALL 57 



or ovoid changes to a spherical form, and the long cilium becomes 

 more plainly visible than before, dragging behind passively. Thi 

 last described feature has been reported for the motile spores of 

 various Chytridiaceae. Periods of activity alternate with periods 

 of passivity, during which the vacuolated condition is very evident. 

 The fat drop is visible only during the active periods. Barrett 

 (4) and Butler (6) have observed pulsations of the vacuoles in 

 the spores of Olpidiopsis at this stage. 



The fat drop is the most prominent internal feature of the 

 active zoospore. It may be seen to shift rapidly when the zoo- 

 spore is in motion. After a period varying from a few minutes 

 to several hours, terminated by sluggish amoeboid movements, 

 the zoospore comes to a final rest and soon disintegrates. It 

 seems likely that the refractive body so commonly observed in 

 the zoospores of the Chytridiaceae is a drop of fat occupying a 

 vacuole. Atkinson (2) observed the presence of a prominent fat 

 drop in the zoospore of Rhizophidium brevipes. 



Amoeboid movements of zoospores have frequently been men- 

 tioned by investigators of the Chytridiaceae. Schenk (30) ob- 

 served this phenomenon as early as 1858. Daxgeard (8) noted 

 that the zoospores of Chytridium xylophilum creep like amoebae. 

 Busgen (5) observed similar movements in his study of Clado- 



chytrium Butomi. 



I did not directly observe the exit of the large zoospores from 

 the sporanges, but they were seen in considerable numbers moving 

 slowly about in the water, remaining close to the sporanges from 

 which they had emerged. The content of these large zoospores 

 appears to be more granular than that of the smaller ones, which 

 latter appear hyaline in water. Very soon after their exit the 

 large zoospores are surrounded by the smaller ones. One or several 

 of the latter move swiftly toward a large zoospore and become 

 attached to it. As many as five small zoospores have been seen 

 adhering to one large spore, but in all cases only one remains at- 

 tached. There seems to be no uniformity as regards the point of 

 attachment. The small zoospore which remains attached loses 

 its cilium just at the time of contact. Kusano (17) reported a 

 resorption of the cilium at this stage in Olpidium. After a small 



