60 



THE SIMPLE HOLOCARPIC BIFLAGELLATE PHYCOMYCETES 



Carpenterella sp. (?) 



Text-fig. A. Amoeboid thalli and spherical bodies in sugar 



cane. Drawn from photograph 5B after Carpenter, 



- 4(). 

 Text-fig. B. Two almost equal, paired spherical bodies. 



Drawn from photograph 7, left, after Carpenter, '40. 

 Text-fig. C. Association of a large and a small sphere. 



Drawn from photograph 7, right, after Carpenter, '40. 



Carpenterella Molineq 

 (All figures after Tehon and Harris) 



Text-fig. D. "Thalli in fiber cell showing plasmodial en- 

 largements and bead-like knots." 



Text-fig. E. "Thallus in ray and wood parenchyma cells, 

 showing connections through pits." 



Text-fig. F. "Net-like thallus in parenchyma cell, sending 

 plasmic projections into an adjoining trachea through 

 half bordered pits." 



Text-figs. G to L. "Stages in the formation of the oospore, 

 showing shrinkage of the male cell to form the com- 

 panion cell of the oospore." 



Text-fig. M. "Mature oospore with dense alveolar cyto- 

 plasm, granules, heavy wall, and companion cell." 



dinal groove, laterally biflagellate and isocont, one 

 flagellum directed forward, the other backward in 

 swimming; swimming movement slow in a spiral 

 path, zoospores rotating on their axes. Oospores 

 formed by the fusion of the contents of one or more 

 small thalli (antheridia ?) and an egg cell (?) lying 

 within a rudimentary (?) oogonium; fusion canal 

 fine and delicate; male thalli remaining attached to 

 the oogonium as empty hyaline vesicles or compan- 

 ion cells ; germination unknown. 



This genus includes a single species, P. vernalis, 

 which combines in its life cycle many of the char- 

 acters of the Olpidiopsidaceae, Lagenidiaceae, 



Saprolegniaceae, and Pythiaceae. It is strikingly 

 similar to Ectrogella, A phanom i/copsis , Achli/a and 

 Saprolegnia in the method of formation and be- 

 havior of the zoospores, but differs from these gen- 

 era, according to Couch, by the appearance of its 

 protoplasm which has a pale whitish fatty gleam like 

 that of Lagenidium, Myzocytium, Olpidiopsis, etc. 

 In type of sexual reproduction it resembles to some 

 degree Olpidiopsis sehenkiana, but differs from this 

 species by the presence of periplasm in the oogo- 

 nium. By the latter character it resembles species of 

 P y thiu m. 



Pythiella vernalis parasitized Pythium gracile 

 and P. dicti/osporum which in turn are parasitic in 

 species of Spirogyra. As is shown in figure 1 the 

 zoospore of P. vernalis comes to rest on the Spiro- 

 gyra filament, encysts, and then develops a fairly 

 long germ tube which penetrates the algal cell until 

 it reaches the Pythium hyphae within. The latter is 

 then pierced, and the content of the zoospores passes 

 into the host cell as a more or less naked globule of 

 protoplasm (fig. 1), like that of Olpidiopsis, Ectro- 

 gella, etc. The zoospore ease and penetration tube 

 remain behind and persist for a long time after in- 

 fection. The young parasite assumes a spherical or 

 oval shape in the Pythium hyphae (fig. 2), but it is 

 not certain that it possesses a well-defined wall in 

 the early stages of development. Couch believed that 

 it may be enveloped by a membrane at this stage, but 

 his figures do not show it. No evidence of amoeboid 

 movement or migration of the young parasite has 

 been observed. As the thallus develops, the host hy- 

 phae enlarge in the region of infection so that 

 broadly oval, spindle-shaped and spherical swell- 

 ings or galls are produced (figs. 2, 13, 18-23). How- 

 ever, the host does not form cross septa and delimit 



