PYTHIUM 



101 



to such crop plants as tobacco, cabbage, and tomatoes being 

 grown in seed beds. It is probable that P. idtiimm?, when isolated 

 from diseased seedlings, has been wrongly identified in some in- 

 stances as P. de baryamnn. Although P. idtlmiim does not form 

 zoospores, its sporangia germinate directly, that is, by germ tubes, 

 and its antheridia are androgynous. 



Fig. 30. Sonmierstorffia sp'inosa, parasitizing the rotifer Monostyla attached 

 to a filament of the alga Rhizoclonium. (Adapted from Sparrow.) 



Pythiimiaphajjiderinatinn, described by Edson (1915) as Rheo- 

 sporangknn aphaniderviatum, is the cause of a seedling- and root- 

 rot disease of sugar beets and radishes. It has been found to 

 attack also the seedlings of various other species. Its cytology 

 and developmental history, as reported by Edson, agree with that 

 known to characterize Pythium. Similarly Zoophagiis insidians, 

 described by Sommerstorff (1911) as a predator on rotifers, ap- 

 pears to belong to the Genus Pythium instead. 



In Pythium, as usually encountered, the protoplasm passes in 

 an undifferentiated state into a vesicle at the tip of the exit tube, 



