988 AQUATIC PHYCOMYCETES 



lining a large central vacuole. Upon its disappearance the spore initials 

 swell and fill the sporangium, though the cleavage lines remain sharply 

 defined. No special forcing apparatus is formed, the valves merely being 

 pushed apart by the expanding thallus. The zoospores resembled the 

 primary type found in Ectrogella bacillariacearum. Secondary zoospores 

 were not observed. 



Lagenidium brachystomum Scherffel 



Arch. Protistenk., 52: 21, pi. 2, figs. 70-85. 1925 



(Fig. 80 A-C, p. 987) 



Thallus tubular, very thin-walled, predominantly unbranched and 

 150—250(jl long by 4-7.5 u, in diameter, or with short or, rarely, somewhat 

 elongate finger-like branches running parallel with the main axis, infec- 

 tion tube occasionally persistent, forming a single sporangium with a 

 very short thick-walled cylindrical discharge tube which functions also 

 as a forcing apparatus between the girdle bands of the host; zoospores 

 few (from two to four) or numerous, grape-seed-like, laterally biflagel- 

 late, 6-8 \x long by 4 u. wide, formed in a vesicle at the orifice of the 

 discharge tube; plants dioecious, gametangia resembling the sporangia; 

 resting spore lying loosely in the female gametangium, spherical or 

 broadly ovoid to oblong, 1 1-24 u, long by 6-10 u, broad, colorless, with a 

 moderately thick smooth wall and with one or two large globules in the 

 dense contents, germination not known. 



Parasitic in Synedra ulna, Cymbella cymbiformis var. parva, Gompho- 

 nema constriction, Nitzschia linearis, Scherffel (he. cit.), Hungary; 

 Synedra sp., Couch (1935b: 385, figs. 20-21), United States. 



The species, according to Scherffel, differs from Lagenidium enecans 

 in forming typically an unbranched sporangium (Fig. 80 A) and a very 

 short discharge tube which is not prolonged extramatrically (Fig. 80 B). 

 Further, the valves of the diatom are not split apart but forced. 



Mixed infections of this species, with Ectrogella bacillariacearum 

 and E. monostoma, may occur in Synedra ulna. When this happens the 

 type of zoospore discharge, the character of the contents, and the 

 method of exit of the discharge tube are used in differentiating the 

 members of the complex. 



