816 AQUATIC PHYCOMYCETES 



This appears to be the most common and widespread of the marine 

 fungi. Considerable information has been collected with respect to its 

 development and something is known of its cytology. Further study of 

 the behavior of the zoospores is needed, however, particularly to ascertain 

 whether or not they are diplanetic when they swarm directly from the 

 sporangium without previous encystment. 



Aleem (1950a) has indicated that the zoospores are more or less 

 rounded or slightly pyriform, with two unequal flagella, one about four 

 times the diameter of the zoospore in length, the other two to three 

 times. The flagella arise at the same end of the cell (anterior?) and are 

 inserted slightly apart. 



The zoospore (Sparrow, 1934c) upon coming to rest on the surface 

 of Striaria encysts and produces a tenuous germ tube which penetrates 

 the wall of the host and through which the protoplasm of the zoospore 

 flows (Fig. 61 A, p. 818). After discharge the empty cyst of the spore 

 remains adherent, at least for a time, to the wall of the alga. Once 

 infection is accomplished, the amoeboid-appearing plasma of the fungus 

 increases in size and, though at first irregular in shape and scarcely 

 distinguishable from the algal protoplasm, ultimately becomes a some- 

 what spherical refractive mass, which often occupies the center of the 

 cell of the Striaria (Fig. 61 B-F). The cell is apparently stimulated to 

 abnormal growth very early in the course of the infection. 



The chloroplasts of the infected cell soon become discolored and 

 disintegrate, and the residue of such material not utilized by the fungus 

 may usually be observed as a peripheral brownish-green layer around 

 the outside of the thallus. The wall of the host is eventually ruptured 

 by the constantly enlarging fungus, which then protrudes into the outside 

 medium (Fig. 61 K-M, p. 818). This liberation of the parasite from a 

 wholly endobiotic existence is initiated by the formation on the thallus 

 of one or, usually, two broad apical or subapical papillae which 

 penetrate the algal wall (Fig. 61 G-J). Subsequent expansion and 

 elongation of the parasite, if more than one papilla is formed, causes a 

 part of the algal wall between the papillae to be carried up between the 

 protuberances. The remainder of the wall persists around the more 

 proximal portion of the sporangium. 



The thallus is at first uninucleate according to Lowenthal (1905). 



