320 AQUATIC PHYCOMYCETES 



warty wall, formed sexually after conjugation with a small male thallus 

 by means of a tube or asexually at the tip of a fusiform persistent germ 

 tube, at germination functioning as a prosporangium. 



Parasites of fresh-water algae. 



According to Canter's (1946) account of Dangeardia mammillata, 

 the zoospore encysts on the surface of a coenobium, produces a fine 

 germ tube which grows through the mucilage sheath of the host to 

 the nearest cell. After it reaches this it broadens, proximally to distally, 

 until the thallus is almost cylindrical. The base continues to swell, 

 and the whole becomes a flask-shaped sporangium, which is imbedded, 

 except for the apex of the neck, in the sheath. The rhizoids are numerous, 

 short, usually unbranched, 3 u, long, and arise in a tuft from the spo- 

 rangial base to penetrate the host cell. Zoospores range from twenty 

 to one hundred and emerge separately, squeezing out of an opening 

 formed by the deliquescence of the apex. As soon as the first spores 

 are freed, the remainder become active and swarm over each other 

 within the sporangium. A sporangium empties within 5 to 10 minutes 

 after opening, but does not at once collapse. It shrivels up fairly soon 

 however. 



Zoospores in Dangeardia mammillata are of two kinds. Some are 

 spherical, 2-5 u. in diameter, with a conspicuous oil globule surrounded 

 by less dense protoplasm; others are often somewhat oval, 3.5 u, by 

 1.8 [i, and appear slightly flattened. The latter contain, in addition to 

 the globule, a "minute, rod-shaped, oscillating granule." All of them 

 have a single posterior flagellum. Only one kind of spore is formed 

 in any one sporangium. In her November collections Canter found only 

 zoosporangia, but by mid-December resting spores had appeared. These 

 are sexually formed, by the union of a larger, flask-shaped thallus 

 (female) almost identical with the zoosporangium and a smaller one 

 (male) resembling a young asexual sporangium. Evidence indicates 

 that the male derives only from the zoospore with the moving granule, 

 but further work with single-spore cultures is needed to substantiate 

 this. 



The young resting spore cannot only be recognized by an associated 

 male thallus but by its clavate germ tube and oily contents. The male 

 germ tube, which is rarely branched, contacts directly the swollen base of 



