PERONOSPORALES 1031 



bear one to five tenuous, predacious tentacles at the apex. Cytoplasm 

 in the tips of the short lateral hyphae highly refractive; tentacles, 10-17 u. 

 in length and 1.5 to 2 (x in diameter, and terminated by a small knob. 

 Conidia or gemmae produced at the end of the long hyphae in acropetal 

 succession, 40-80 \x in length and 3-6.5 \x in diameter. Growing loosely 

 epiphytic in Nitellaflexilis; predacious and parasitic on species of Mon- 

 ostyla, Diostyla, etc." (Karling, he. cit.). 



United States. 



Prowse (1954b) concurs with the view that since no zoospores were 

 observed, the organism might in fact be a conidial Phycomycete. This 

 is contrary to Middleton's (1952) opinion. 



No sexual organs have been found. 



PYTHIUM Pringsheim * 



Jahrb. wiss. Bot., 1 : 304. 1858 



(Figs. 83, p. 1016; 84, p. 1018; 86, p. 1030; 87, p. 1032) 



Mycelium well developed, consisting of much-branched hyphae, oc- 

 casionally bearing appressoria, sometimes forming tangled complexes, 

 irregular toruloid elements, and chlamydospores; zoosporangium either 

 entirely filamentous and undifferentiated from the vegetative hyphae, 

 simple or branched, acrogenous or intercalary, or consisting of a series 

 of basal complex lobulations and a filamentous discharge tube, or a well- 

 defined sphaeroidal structure sharply distinct from its supporting hypha 

 and acrogenous, intercalary or laterally sessile, with an emission tube 

 of variable length, sometimes internally proliferous; zoospores some- 

 what reniform, each containing a single vacuole and with two opposite- 

 ly directed flagella of approximately equal length emerging from a 

 shallow longitudinal groove, expelled from the sporangium as an 



of Pythium marinum Sparrow, showing plerotic oospore with thin wall and 

 single diclinous antheridium with abruptly tapering apex. K. Cluster of ap- 

 pressoria of Pythium adhaerens attached to an algal wall. 



{A, F, H, Middleton, 1943; B-D, I, K, Sparrow, 1931b; E, G, Matthews, 

 1931;/, Sparrow, 1934c) 



1 See Phytophthora, note (p. 1051). 



