CHYTRIDIALES 551 



long), with a latero-basal globule and greyish protoplasm with a few 

 minute granules. Resting spore sexually formed. Male oval to elongate 

 oval (2 x 3.5-2 x 6 u.) makes contact with a female of more or less 

 similar size by means of a conjugation tube up to 16[x long. Resting 

 spore elongate oval, 5.5-17 \l long and 3-6 \i high. Wall thick, smooth, 

 colourless, content when mature a single large globule. Both male and 

 female bearing rhizoids. Germination unknown" (Canter, loc. cit.). 



Parasitic on Ankistrodesmus sp., Elaktothrix gelatinosa, in plankton. 

 Great Britain. 



Here, the zoospore makes its way through the very broad gelatinous 

 colonial envelope and comes to rest on the host cell. In sexual reproduc- 

 tion the male may sometimes be nearly adnate to the female. Conjugat- 

 ing thalli seemed always to be originally of the same size. 



Zygorhizidium melosirae Canter 

 Ann. Bot. London (N.S.), 14: 283, fig. 13. 1950 



"Thallus epibiotic, stalked or sessile, sporangium ovate, 7 14 [x high 

 by 5-10 [i. in diameter with 6 to 30 zoospores, dehiscing by a lid. Zoo- 

 spores spherical, 2.8-3.3 \x in diameter, with a large oil globule (0.9 u,), 

 and posterior fiagellum. Intramatrical rhizoid unbranched or sparingly 

 branched, not tapering. Resting spores ovate, 9.5-10 \x high by 6-7.5 \x 

 broad, wall smooth, the content with a few large globules; arising from 

 fusion of the contents of a small male with a larger female cell by a 

 conjugation tube, 0.7-7.5 \x long. Germination unknown" (Canter, loc. 

 cit.). 



Parasitic on Melosira italica subsp. subartica, Great Britain ; Melo- 

 sira sp., Paterson (comm)., United States. 



Whenever a gelatinous sheath surrounds the host filament, the zoo- 

 spore rests on the outer surface and germinates. Hence, sporangia from 

 such zoospores are stalked. 



Zygorhizidium planktonicum Canter ] 

 Trans. Brit. Mycol. Soc, 36: 34, fig. 1 E-M, fig. 5 M-X. 1953 

 (Fig. 11 A-B, p. 110) 

 "Thallus monocentric consisting of an epibiotic obpyriform [pyriform] 

 sporangium (4-9 [x high; 3-8 y. broad) whose apex functions as an oper- 

 1 Paterson (Trans. Brit. Mycol, Soc, 41: 457. 1958) considers this species sy- 

 nonymous with the preceding one. 



