10 
Bulletin 91. 
tification, show that it belongs to the well known species, * Cor- 
ticium vagum B. & C., but its parasitic mode of life, size and 
shape of spores, have been considered of sufficient distinction for a 
new variety and it is designated as Corticium vagum B. & C. var. 
solani Burt. This stage has been observed only on or near green 
potato plants. The fruiting layer does not adhere firmly to the 
stem and cracks and falls off very easily when the stem becomes 
too dry, consecpiently all traces of it usually disappear soon after 
the death of the plants. 
From 225 pieces of stems covered with the fruiting 
layer placed in agar, 203 developed pure cultures of the Rhizoc- 
tonia ; 15 Fusarium and 7 Altenaria. Cultures from this fruiting 
layer have been carefully watched during the past two years and 
they resemble in every way the pure cultures developed from the 
Sclerotia and pure cultures developed from liyphse taken from a rot¬ 
ten tuber. All attempts in the laboratory to induce this fungus to 
develop spores on various culture media, have failed. However, 
if diseased tubers are planted in a suitable place they will produce 
plants on which the fruiting layer grows and develops spores 
abundantly. 
The spores fall as soon as they are mature, consequently it is 
difficult to obtain cultures by the usual methods. The following 
plan was finally devised, which has proven quite satisfactory: 
A stem on which the fruiting layer had developed was suspended 
over a petri dish containing agar. The stem and dish were then 
covered with a sterile bell jar. (See Plate II.) 
Spores show considerable difference in their germinating 
power, frequently they germinate within a few hours after 
they fall on agar. Each spore usually pushes out one 
germ tube; occasionally, however, two tubes are formed. The 
tube as it emerges from the spore is constricted and reaches its 
normal size at from 10 to 15 mm. from the spore. The growth 
is comparatively slow during the first two days and septa are only oc¬ 
casionally observed. About the third day side branches develop and 
the septa become more noticeable. By the fifth or sixth day the 
hypse have taken on many of the Rhizoctonia characteristics and 
branch freely. Sclerotia usually form on potato plugs in twelve 
days. 
Over sixty pure cultures of Rhizoctonia have been obtained 
from the spores of the corticium stage and these cultures resemble 
those obtained from the sclerotia on tubers and those made from 
seed tubers rotted by the hyphse of Rhizoctonia. 
* This fungus agrees well with the description of Hyponochus solani, 
Prill. & Dell., but several specimens of it were sent to Dr. E. A. Burt, and after 
carefully examining them he has concluded that it is a variety of Corticium 
vagum B. & C., for which he has suggested Corticium vagum B. & C. var .solani. 
