SAPROLEGNIALES 813 



thallus (Fig. 63B), and the protoplasm of the receptive thallus is dif- 

 ferentiated into periplasm and ooplasm. At maturity the resting spore 

 has a distinct wall of its own and is loose within the container. 



The sequence of protoplasmic changes preceding zoospore formation 

 exhibited by Pythiella is similar to that in Ectrogella, in which strong 

 vacuolization, "balling," and homogeneous and segmented stages occur. 

 Because of this Couch (pp. cit.) concluded that the two genera are 

 closely related. There is no doubt that placing the genus in the Sapro- 

 legniales expresses its proper relationship, rather than the former alliance 

 with Olpidiopsis in the Lagenidiales (Sparrow, 1943). 



Although some doubt will exist until a sexual stage is found, Ectro- 

 gella besseyi Sparrow and Ellison, both in structure and host plant, 

 exhibits a closer affinity to Pythiella than to Ectrogella. For this reason, 

 the original generic description of Pythiella has been made somewhat 

 more general (but not modified in essentials) to include species on hosts 

 other than Pythium. 



KEY TO SPECIES OF PYTHIELLA 



Sporangium spherical or rarely subspherical; in hyphae of Pythium 



P. vernal is, p. 813 

 Sporangium somewhat tubular, often lobed; in Olpidiopsis 



P. besseyi, p. 814 



Pythiella vernalis Couch 



Mycologia, 27: 160, figs. 1-27. 1935 



(Fig. 63 A-B, p. 824) 



"Sporangia developing in the threads of Pythium, spherical or rarely 

 subspherical when mature, without mycelium and rhizoids; causing the 

 formation of a distinct gall in the Pythium thread, usually one sporan- 

 gium in each gall though two, three, or four may not uncommonly 

 occur; 10-30 [j. thick, emptying through a long tube up to 50 \i long 

 and about 4 ;x thick; on some sporangia several tubes may be formed 

 (as many as five), some of which may be branched. Spores diplanetic, 

 encysting after discharge, at the tip of the sporangial tube, emerging 

 from the cysts after about an hour, elongated with a longitudinal groove 

 and with two cilia; spores 3.7-4 \i thick. In swimming the active cilium 



