764 AQUATIC PHYCOMYCETES 



are formed. Eventually the sporangial rudiment, which has grown more 

 in thickness than in length, is cut off by cross walls from the rest of the 

 thallus and one or more papillae are formed. The droplets within its 

 contents coalesce to form the globules of the mature zoospores. Dis- 

 charge of the spores already moving within the sporangium was not 

 observed with certainty. 



IMPERFECTLY KNOWN GENUS OF THE HYPHOCHYTRIALES 



? REESSIA Fisch 

 Sitzungsber. Phys.-Med. Soc. Erlangen, 16:41. 1884 



"Thallus intramatrical, monocentric, holocarpic; more or less naked 

 (but immiscible with, and distinct from, the enveloping host proto- 

 plasm) when young, but becoming invested with a distinct wall at matu- 

 rity; amoeboid or stationary during the vegetative developmental stages. 

 Zoosporangia usually solitary, hyaline and smooth, oval or spherical 

 with one elongate cylindrical exit tube which may project considerably 

 beyond the surface of the host cell. Zoospores oval or spherical and 

 hyaline with a conspicuous refractive globule; emerging fully formed 

 and swimming directly away or lying quiescent for a few moments in a 

 mass at the mouth of the exit tube. Gametes when present similar to the 

 zoospores, fusing in pairs to form bifiagellate motile zygotes which 

 infect the host cell, grow in size, and become resting spores. Resting 

 spores spherical or oval, yellowish or light brown, with a smooth thick 

 double-layered wall and one to several large refractive globules; trans- 

 formed directly into a zoosporangium in germination" (Karling, 1943: 

 642). 



Parasitic in species of Lemna. 



In addition to the two Lemna parasites described in the following 

 pages, Fisch cited a third species, Reessia cladophorae, about which 

 practically nothing is known. It has been referred to Olpidium by Fischer 

 (1892) and Minden (1915). 



The genus Reessia (R. amoeboides) was established by Fisch (1884a: 

 41) for an organism inhabiting Lemna. The zoospore was said to pen- 

 etrate the cell of the host by its flagellum. Inside the cell the thallus 

 remained amoeboid for a time, then surrounded itself with a wall, 



