8 
Bulletin 91 . 
DEVELOPMENT OF FUNGUS. 
The fungus is truly a parasitic-organism, flourishing in heavy, 
wet soils; and our observations during the past three years show 
that it produces fruit only on or near the living tissues of plants. 
Its development may be divided into the following stages: 
The Rhizoctonia Stage .—Two forms of liyphal growth are 
constantly associated with the injuries resulting from this fungus 
—a light and a dark colored. The light form usually develops 
deeper in the tissues and is more actively parasitic and frequently 
produces a wet rot of the stem and old seed tubers, while the col¬ 
ored, or rhizoctonia proper develops more freely on or near the 
surface of the roots and tubers. The colored form is also fre¬ 
quently found growing in the soil some distance from the plants 
and is constantly associated with the fruiting stage of this fungus. 
(See Plate V., 1 .) 
The Sclerotia Stage .—The hyphae give rise to dark irregular¬ 
shaped bodies which are made up of a mass of large, close-septate 
hyphae.' (See Plate V., 2 .) These bodies are known as sclerotia. 
Experiments show that this stage is well adapted for tiding the fun¬ 
gus over unfavorable periods, and that it is a prominent factor in 
the dissemination of this disease. The sclerotia resemble closely 
particles of soil and are frequently mistaken for scales of dirt ad¬ 
hering to the tubers. When infected tubers are used for seed these 
Sclerotia produce hyphae which in turn injure and often kill the 
plants. 
The Corticmm Stage .—The young plants developed from seed 
tubers, which are more or less covered with the sclerotia stage, 
usually have their subterranean parts covered with a network of 
dark hyphse. This dark network advances with the growth of the 
plant until it reaches the surface of the ground, where it changes 
into a grayish white fruiting layer, frequently entirely surround¬ 
ing the base of the green stem and often extending up the stem 
for a distance of four inches. (See Plate I., 3 .) The tips of the 
outermost hyphae of this fruiting layer develop into basidae, which 
usually bear from two to four stregmata (See Plate III.), but in a 
few instances six have been observed. The spores are hya¬ 
line and usually ovate in form with apiculate bases; fifty spores 
taken just as they occurred on a green stem gave an average 
measurement of ten by six u. But mature spores after they had 
fallen measured twelve by eight u, the largest measuring fifteen 
by thirteen u, and the smallest nine by six u. 
The hyphal characters, form of basidae, and structure of fruc- 
