510 AQUATIC PHYCOMYCETES 



Sporangium sessile, rarely on a short isodiametric stalk, upright or 

 slightly tilted, broadly or narrowly ovoid, occasionally obovoid, 18-40 

 \x high by 15-32 \x in diameter, with a flattened apex bearing two 

 opposite solid slightly incurved sharp teeth up to 6 \x long by 2-4 \x 

 at base (rarely one), wall smooth, colorless; rhizoids arising as single 

 isodiametric filaments from either side (rarely one side) of a broadly 

 fusiform, rarely spherical, subsporangial swelling 7-15 [j. in diameter 

 by 3-6 jo. high, remaining isodiametric, rarely branched, and about 2-2.5 

 (j. in diameter save when meeting a cross wall, where they expand to 

 4 \x or more, strongly polyphagous, penetrating as many as forty or 

 more cells of the alga, which they stimulate to form protective thick- 

 enings of the transverse walls; zoospores spherical, 5 \x in diameter, 

 with a slightly eccentric colorless strongly refractive protruding globule, 

 flagellum 27 \x long, upon the dehiscence of a slightly convex round 

 operculum 10-12 jx in diameter escaping fully formed in a compact 

 temporarily vesiculate motionless group, suddenly assuming violent 

 individual motion, eventually freeing their flagella and hopping away, 

 movement intermittently amoeboid; resting spore not known with 

 certainty. 



Parasitic on Tribonema bombycina, Wille {he. cit.), Sweden ; Scherffel 

 (1925b: 32, pi. 2, figs. 63-80), Hungary; Sparrow (1939a: 124), United 

 States; coll. Odam, communication and drawings, Sparrow (1957a: 

 532), Great Britain; Tribonema bombyeina, Rieth (1951: 259, figs. 

 1-14), Germany. 



Scherffel found two types of resting structures associated with the 

 sporangial stage of this species, but neither can be said with certainty 

 to belong to it. The first was epibiotic, sessile, spherical or subspherical, 

 and 9-16 \x (mostly 14 [j.) in diameter exclusive of the ochre-yellow 

 epispore, which was 2-3 \x thick, irregular, and covered with blunt 

 knoblike protuberances; the endospore wall was smooth and 1.5-2 \x 

 thick, and the fatty plasma of the contents bore a single colorless globule 

 8-1 1 [jl in diameter. At the base was a smooth spherical or clavate empty 

 structure which presumably functioned as a contributing cell in a sexual 

 process. The second type of resting spore occurred singly within the 

 horned sporangium; it was spherical and covered with a network of 

 ridges. 



