HYPHOCHYTRIALES 763 



Hyphochytrium hydrodictii Valkanov 



Arch. Protistenk., 67: 122, figs. 1-11. 1929 



(Fig. 56C-E, p. 761) 



Vegetative system arising as a lateral outgrowth from opposite sides 

 of the rudiment of the sporangium, broad, tubular, not tapering, rarely 

 branched, extending through many cells; sporangia endobiotic, inter- 

 calary, from one to several (up to three) on the thallus, when single, 

 sporangium formed from the primary swelling produced by the infecting 

 zoospore, the cyst of which is persistent, when several, sporangia formed 

 as well from secondary swellings of the vegetative system from which 

 they are cut off by cross walls at maturity, broadly fusiform or occasion- 

 ally somewhat irregular and gibbose, with a smooth, thin, colorless 

 wall, forming a single functional papilla which pierces the host wall 

 (rarely two or more nonfunctional papillae), method of opening not 

 observed; zoospores ovoid with a broad rounded apex, a single eccentric 

 colorless globule, and a long anterior fiagellum, capable of amoeboid 

 motion, from fifty to one hundred or more in a sporangium, individual 

 motion initiated within sporangium; resting spore terminal or inter- 

 calary, fusiform, with a thicker inner wall, contents charged with nu- 

 merous droplets of uniform size, upon germination forming a single 

 discharge papilla. 



Parasitic on young cells of Hydrodictyon reticulatum, Bulgaria. 



According to Valkanov the development of the fungus is as follows: 

 The zoospore, after coming to rest on the host and encysting, penetrates 

 the wall and produces within the alga a spherical outgrowth. This 

 growth as it expands elongates parallel to the long axis of the Hydro- 

 dictyon cell (usually in opposite directions from the point of infection) 

 and results in the formation of a broad tubular hypha-like generally 

 unbranched structure (Fig. 56 C). The rudiment of the sporangium is 

 recognizable from the beginning as the rather broad fusiform structure 

 that is first laid down by the parasite and from the opposite sides of 

 which the rhizoidal elements emerge. Later, other sporangia may be 

 produced by secondary swellings of the "hyphae." It is probable that 

 the primary reproductive structure absorbs host material, in much the 

 same fashion as does an Olpidium, at least until the vegetative organs 



