630 



Journal of Agricultural Research 



Vol. VI, No. 17 



They are from 15 to 25/i in diameter, averaging about 22ju. The anthe- 

 ridium (fig. i, b) is borne either on the same filament as the oogonium 

 or on an adjacent filament. If arising from the same filament ic may 

 be borne directly below the oogonium or some distance below. More 

 than one antheridium was sometimes found attached to an oogonium. 

 The oospores (fig. 1, b) are smooth, spherical, and thick -walled. They 

 are from 14 to io^u in diameter, average i6ju, and do not fill the oogonuim. 

 These measurements of the oogonia, oospores, and conidia all agree 

 closely with those of P. debaryanum, as given by Butler. A culture of 

 P. debaryanum used by Mr. C. P. Hartley in his studies on the damping-off 

 of pine seedlings was obtained from the Office of Forest Pathology. This 

 culture was a subculture of a strain which had been isolated from rotten 



Fig. i. — Microscopical appearance of Pyihium debaryanum isolated from potatoes aflected with potato 

 leak: a, cell of a potato tuber showing fungus filaments therein; b, oogonia and antheridia; c, mycelium; 

 d, germinating conidia. 



potato by Kdson (6) used by him in his studies on seedling diseases of 

 sugar beets and then turned over to Hartley. This fungus agreed very 

 closely with the Pythium sp. isolated from the leaky tubers in size of the 

 conidia, oogonia, and oospores, habits of growth, and general appearance. 

 Inoculated into potato tubers it produced a rot similar in all appearances 

 to that produced by the fungus obtained from the leaky potatoes. 

 It would seem, then, from the evidence above cited that the fungus 

 isolated from the leaky potatoes in this study is the same as Hesse's 

 Pythium debaryanum (7). 



CULTURAL STUDIES 



Cultures of the fungus were made on various kinds of media. The 

 fungus grew well on beef, corn-meal, oatmeal, string-bean, Lima-bean, 

 and potato agars, and Pfeffer's plant agar, potato plugs, and stems of 

 Melilotus alba. Conidia and oogonia were formed when the fungus was 



