70 AQUATIC PHYCOMYCETES 



a similar type of sexuality also occurs in Micromyces longispinosis, 

 an algal parasite belonging to the same family (Synchytriaceae). 



Sexuality has been noted in several members of the Phlyctidiaceae. 

 Gimesi (1924) stated that in Phlyctidium eudorinae the resting spore 

 is formed after terminal or lateral fusion of two isogamous gametes, 

 one of which has previously come to rest and germinated and the other 

 has become encysted on it. Hanson (1944a) shows a similar type of 

 sexuality is present in Loborhiza (Fig. 4 U, p. 72). In resting-spore 

 formation in Dangeardia mammillata, Canter (1946) found that union 

 typically occurs between a large flask-shaped thallus ("female"), similar 

 in appearance to a zoosporangium, and a small one ("male"), resemb- 

 ling a young undeveloped sporangium. The germ tube of the male, 

 which rarely branches, makes contact with the swollen base of the 

 female. In some instances males were lacking, in which case the resting 

 spores apparently developed parthenogenetically. In several species 

 of Rhizophydium a sexual process of a somewhat different nature has 

 been reported (Scherffel, 1925b; Couch, 1932, 1935a; Sparrow, 1933c, 

 1936a, 1939a; Canter, 1950a). In certain species, as R. goniosporum, 

 R. ephippium, R. planktonicum, R. sphaerocystidis, and R. hyalobryonis, 

 the male gamete (rarely two) attaches itself directly to the larger, epi- 

 biotic, receptive thallus, which is already established on the host. Com- 

 munication is made between the two, and the contents of the small 

 encysted male pass into the thallus. There is no loss of identity of the 

 two gametangia, and after the receptive structure, which now contains 

 the two gametes, becomes transformed into a thick-walled resting 

 spore, the empty cyst of the male remains adherent to it. Indications 

 are that sometimes, at least, the receptive thallus may undergo consider- 

 able enlargement before contact with the male is made. At other times 

 like-sized swarmers settle down in pairs on the surface of the host 

 and establish themselves. One of them apparently enlarges at a gi eater 

 rate than the other, receives the contents of the smaller one, and be- 

 comes transformed into the resting spore. In R. couchii (Couch, 1932; 

 Sparrow, 1933c) the swarmers which give rise to the gametangia are 

 at first identical in size and shape (Fig. 4 G, p. 72). After a period 

 of swarming they come to rest on the surface of the alga in groups 

 of four to ten or more. Each of two adjacent encysted swarmers pro- 



