66 AQUATIC PHYCOMYCETES 



It seems logical to suppose, considering the efficiency of oil as a 

 concentrated source of energy, that the globule provides the material 

 necessary for the activity of the flagellum, and, after encystment, 

 for the production of the penetration tube and the very young thallus. 

 By this means food is assured the developing plant until such time as 

 contact with nutrient materials in the substratum has been estab- 

 lished. Indeed, early in the formation of the thallus the globule or- 

 dinarily fragments and, possibly owing to the resultant increase in 

 surface, is soon absorbed into the cytoplasm. 



The posteriorly directed flagellum is apparently attached to the rear 

 of the body in all forms except Olpidiomorpha (Scherffel, 1926b), 

 Zygorhizidium verrucosum Geitler (1942), and Pleotrachelus wildemani 

 Ingold (1952), in which it is subapical. For further details concerning 

 flagella, see "Zoospore, , ' p. 7. 



The type of movement exhibited by the chytrid zoospore may be 

 either free-swimming or amoeboid, a fact early noted by Schenk 

 (1858b). During swimming the motion may be extremely erratic, the 

 zoospore sometimes hopping and at other times gliding steadily for 

 a while then suddenly going into a series of short convulsive springs. 

 The hopping or dancing type of movement has been considered highly 

 characteristic of the chytrid zoospore, particularly by Scherffel (1925a, 

 1926b, etc.), but, like the amoeboid type, it is not found in all species. 

 Often the movement may consist solely of extremely rapid darting with 

 frequent pauses and changes of direction; at other times it is a smooth 

 even gliding, accompanied by a gentle rocking or an occasional ro- 

 tation of the body. During sudden pauses the body may undergo re- 

 markable amoeboid changes of shape and become strongly vacuolate. 

 It then creeps around for varying periods on bits of substrata, its pas- 

 sive flagellum trailing behind. No ingestion of solid materials during 

 such periods has ever been convincingly described. In resuming the 

 swimming type of movement the body of the zoospore all at once be- 

 comes rounded, the flagellum vibrates again, and the spore darts off. 



The duration of the period of motility of the free-swimming zoospore 

 no doubt depends upon the species of chytrid, the vitality of the in- 

 dividual spore, and the conditions prevailing in the medium at the 

 time. The amount of oxygen, the temperature, and freeness from noxi- 



