i6o Journal of Agricultural Research voi. iv, no. 2 



beet among its hosts. The fungus is so well known that a description 

 here is superfluous. It is very readily secured in pure culture and is 

 easily carried upon media (PI. XVI, fig. i). It grows especially well with 

 long-continued vitality upon string-bean agar. The sexual fruiting 

 bodies are quite common in Petri-dish cultures upon this medium, but 

 are rarely met with in tube cultures. The asexual conidia, as well as 

 oospores, are formed abundantly when the fungus is grown in water 

 upon sugar-beet seedlings in Petri dishes. The cultures obtained through- 

 out the experiments were invariably identified by fruiting bodies, and 

 the same method was applied in proving up the cultures recovered from 

 artificial inoculation. Suspected seedlings were treated in bichlorid of 

 mercury, rinsed in water, and plated upon the acid synthetic agar pre- 

 viously mentioned (p. 137). When growth developed, the mycelium 

 was examined through the bottom of the Petri dish by inverting the plate 

 upon the stage of the microscope. If no septa were visible, the seedling 

 was transferred to a sterile Petri dish after a subculture had been made 

 from the growth. Sterile water was added to the fresh plate con- 

 taining the seedling. In case the growth was Pythium debaryanum, 

 the characteristic conidia developed in great numbers in from 24 to 48 

 hours, to be followed during the next few days by oospores. Direct 

 germination of conidia was often seen and could be very readily induced 

 by adding a fresh beet seedling to the culture. Germination by zoo- 

 spores was not observed, but no special effort was made to induce this 

 type of development. 



The cultures used in the inoculation experiments were all morpholog- 

 ically identical, so far as could be determined. They were secured from 

 the following sources : 



Damped-oflf beets grown at Washington in the greenhouse, 2; at 

 Madison, Wis., in the greenhouse, 6; at Madison in the greenhouse in 

 Utah soil, 3; at Madison in the greenhouse in Michigan soil, 2; damped- 

 off seedlings grown in Utah in the field, i ; grown in Wisconsin in the 

 field, I ; grown in Colorado in the field, i ; damped-ofif pine seedlings from 

 Kansas (contributed by Mr. Carl Hartley, of the Bureau of Plant Indus- 

 try), i; decaying potatoes, isolated in 1909, i. 



Mr. Hartley reported this strain pathogenic to pine seedlings, having 

 produced damping-off with it to the extent of 100 per cent in the seed 

 bed. 



Pythium debaryanum proved to be exceedingly destructive in the pot 

 experiments. When infection was made at the time of seeding, even a 

 temporary stand was seldom secured. Examination showed that the 

 seed germinated, but that the plants were destroyed before they could 

 come up. In many cases the embryo was killed while still within the 

 seed. By delaying the inoculation until the seedlings were well started 

 typical damping-off was produced and the fungus recovered. It was a 

 very common thing to find infection on the tips of the cotyledons. 



