60 AQUATIC PHYCOMYCETES 



until the wall gives way and discharge of zoospores is begun. Wh'le 

 the first spores are ejaculated by internal pressure from within the spo- 

 rangium, this force soon diminishes in intensity and the remainder of 

 the swarmers assume individual motility and creep or swim out. Aside 

 from pressure, another factor influencing discharge may be an increas- 

 ing solubility in water, as the sporangium matures, of the material 

 of the papilla. Then, too, sometimes the zoospores themselves initiate 

 motility within the sporangium and their activity may have an effect 

 on spore discharge. Whatever the cause or causes, the first zoospores 

 ejected appear, as a rule, to be pushed out; the later ones, particularly 

 in large sporangia, either creep out amoeboidly or swim out by flagel- 

 lar action. 



The precise method and the time of formation of the flagellum of 

 the zoospore are not known. Karling (1937b) and Hillegas (1940), 

 who have made perhaps the most extensive cytological study of chy- 

 trids, merely state that it is formed while the zoospores are in the spo- 

 rangium. In many species, for example in Rhizophydium goniosporum 

 (Scherffel, 1925b; Sparrow, 1936a), Phlyctochytrium planicorne, P. 

 bullatum, and P. dentiferum, the fully formed flagellum may be clearly 

 seen trailing behind the body of the spore as it emerges. Scherffel 

 (1926a) believes that in Chytridium schenkii the flagellum of the spore 

 is formed after discharge, during the resting period at the orifice of the 

 sporangium. This is denied, however, by Couch (1938b) for the closely 

 allied C. oedogonii, in which, as well as in R. carpoplrilum, the flagellum 

 is coiled in "watch-spring" fashion around the body of the emerged 

 spore and during the rest period merely falls away from the body, 

 straightens, and eventually assumes its activity. This disposition of the 

 flagellum has been noted in other chytrids also (for example, C. nodu- 

 losum, C. schenkii [Sparrow, 1932b, 1933a]). 



The behavior of the emerged zoospores is probably dependent to 

 some degree upon conditions prevailing in the medium at the time of 

 discharge. Under what appear to be excellent conditions they emerge 

 from the sporangium en masse, without flagellar action, and form a 

 motionless group at the sporangial orifice (Fig. 35 D, p. 583). Here 

 they remain quiescent for a varying period, apparently imbedded in 

 a matrix of mucus or "slime" (Nowakowski, 1876a), which slowly 



