58 



THE SIMPLE HOLOCAUPIC BIFLAGELLATE PHVCOMYCETES 



Parasitic in Cryptomonas ovata in France. 



This species was apparently observed by Dan- 

 geard in 1889 (PI. 1, fig. 15) and mistaken for the 

 endogenous germs of the host. Its outstanding char- 

 acteristic, according to Dangeard ('90), is the radial 

 orientation of the refractive globules in the thallus 

 (fig. 31). The inclusion of this species in Pseudo- 

 sphaerita is obviously questionable, because the thal- 

 lus is expelled from the host as in species of Sphaer- 

 ita. Although Dangeard figured most of the zoo- 

 spores as biflagellate he failed to include this spe- 

 cies in Pseudosphaerita. Nevertheless, it is included 

 here tentatively although nothing is known about 

 the development of the thallus and the type of cyto- 

 kinesis. 



The oval and elongate "nuclei" which Stein 

 (1878, pi. 19, figs. 29, 31) figured in the same host 

 may possibly relate to this species, although no 

 radially oriented refractive globules are shown. 



BLASTULIDIOPSIS 



Sigot, 1931. C. R. Soc. Biol. 108 : 37. 



(plate 17, FIGS. 10-12) 



Thallus intramatrical, unicellular, lobed, pluri- 

 locular, irregular, and holocarpic. Zoosporangia soli- 

 tarv in host cell, hyaline, smooth, irregular, lobed 

 and plurilocular with a low exit papilla. Zoospores 

 biflagellate and isocont, developing completely and 

 swarming in the zoosporangium, swimming directly 

 away after emerging. Resting spores unknown. 

 1 The thallus of this monotypie genus in very simi- 

 lar in appearance to that of Blast ulidium, but the 

 type of infection and thallus development are more 

 like those of species of the family Lagenidiaceae. 

 The zoospore comes to rest on the Cyclops egg and 

 forms a germ tube which penetrates the host wall. 

 The content of the spore does not pass into the host 

 cell as a more or less naked protoplast as in Olpidi- 

 opsis, Ectrogella, etc., but instead the tip of the 

 penetration tube enlarges, elongates, branches and 

 eventually forms the irregular lobed thallus. Sigot 

 did not observe germination, infection and the stages 

 of thallus development in living material, but based 

 his account on studies of fixed and stained prepara- 

 tions. In the early stages of development, the thallus 

 contains numerous small vacuoles (fig. 10) which 

 later fuse to form a large central one. By this time 

 the contents of the host cell have been largely con- 

 sumed, and the parasite usually occupies the entire 

 cavity. After the vacuoles have fused, the more vis- 

 cid, visible part of the protoplasm forms a thin 

 parietal layer in which the nuclei lie (fig. 11). Cy- 

 tokinesis is apparently accomplished by centrifugal 

 cleavage furrows which cut out uninucleate spore 

 rudiments. The latter develop into zoospores which 

 soon begin to swarm within the sporangium. Shortly 

 thereafter the tip of the exit papilla deliquesces, and 

 the zoospores swim out and away. No evidence of 



diplanetism has so far been observed. As is shown 

 in figure 12, the zoospores are oval and slightly 

 elongate with two flagella inserted near the anterior 

 end at which lies a conspicuous refractive globule, 

 similar to that described by Sparrow ('34, '36) for 

 the zoospores of Sirolpidium and Petersenia. 



The taxonomic position and relationships of Blas- 

 tulidiopsis are obscure, since nothing is known about 

 its resting spores. As noted previously its type of 

 development, according to Sigot, is suggestive of 

 species of the Lagenidiaceae, while the appearance 

 of the centrally vacuolate sporangia, swarming of 

 the zoospores within, etc., are similar to those of 

 01 pidiopsis, Sirolpidium, Petersenia and other re- 

 lated genera. 



B. CHATTONI Sigot, I.e., figs. 1-3. 



Zoosporangia solitary, hyaline, smooth, irregular 

 and lobed, size unknown. Zoospores 6 X 8 /j. with a 

 refractive globule at the anterior end; flagella 15— 

 20 ix long, inserted near the anterior end and extend- 

 ing in opposite directions. Resting spores unknown. 



Parasitic in eggs of Cyclops in France, destroy- 

 ing their content but causing no enlargement or divi- 

 sion of the inflated cell. 



PYTHIELLA 



Couch, 1935. Mycologia 27: 160. 

 (plate 15) 



Thallus intramatrical, holocarpic. oval, ellipsoid 

 and spherical ; solitary or up to 1 in a swelling. Zoo- 

 sporangia centrally vacuolate with 1 to 5 simple or 

 branched exit tubes. Zoospores fully delimited in the 

 zoosporangia, diplanetic; primary zoospores aflagel- 

 late, gliding out and encysting at the tip of the exit 

 tube; content of cysts emerging after about an hour; 

 motile secondary zoospores oblong with a longitu- 



plate 15 

 Pythiella vernalis 



Fig. 1. Germinated zoospore with young parasite within 

 Pythium hypha. 



Fig. 2. Beginning of host hypertrophy. 



Figs. 3-7, 9-13. Successive stages of the maturation of 

 a thallus into a zoosporangium, cleavage, zoospore emis- 

 sion, encystment, and emergence from cysts. 



Fig. 8. The so-called esealloped or "balled" stage of 

 sporogenesis. 



Fig. 9. The homogeneous stage following cleavage. 



Figs. 14—10. Successive stages of emergence of the zoo- 

 spore from a cyst. 



Fig. 17. A mature biflagellate isocont zoospore. 



Figs. 18, 19. Young antheridia and oogonia in hypha] 

 swellings. 



Figs. 20, 21. Beginning and completion of plasmogamy. 



Fig. 22. An egg fertilized by two antheridia. 



Fig. 23. Mature oospore within an oogonium and an 

 empty attached antheridium. 



