A T . C. Experiment Station 
11 
Life History of the Causal Organism 
The life cycle of the clover stem rot fungus is relatively simple since 
it possesses only one functional type of spore. It lives for the greater 
part of the year as a saprophyte and can maintain itself in the soil upon 
decaying plant tissues from one year until the next. On the basis of 
difference in appearance and function, the fungus may be regarded as 
possessing three stages. Under normal conditions the first or vegetative 
stage is present during late fall, winter, and early spring, within the 
clover plants causing their death. Invasion of the tissues begins at the 
collar, near the ground level, and extends upward and downward from 
this point of attack. During the same period the fungus continues its 
vegetative growth as a saprophyte in plants which it has killed. As the 
tissues are disintegrated the fungus appears at the surface of the decay¬ 
ing parts and becomes massed together in conrpact black sclerotia, the 
second stage. These sclerotia then remain dormant on the surface of the 
soil or within the soil in the spots left bare by the destruction of the 
clover. Since these sclerotia require only two or three weeks to mature 
they are being formed practically throughout the entire growing period 
of the clover crop. These sclerotia, which contain a reserve of nutri¬ 
ment, remain dormant and serve to carry the fungus over the summer 
season, or until opportune conditions for their growth again prevail. 
During the fall and early winter these sclerotia germinate by the forma¬ 
tion of slender, yellowish-brown stalks. The distal ends of these stalks 
expand into the disc-shaped fruit bodies, which with the stalks constitute 
the apothecia, the third stage. Erom one to a half dozen apothecia are 
developed from each sclerotium, depending upon the size of the sclero- 
tium. The upper or inner surface of these discs is lined with a layer of 
closely aggregated, elongated sacs, or asci, interspersed with the para- 
physes. Eelnn (18) has estimated that there are approximately 5,000 
sacs in one square millimeter of surface, each of which bears at ma¬ 
turity eight ascospores. These ascospores are forcibly discharged, often 
in such numbers as to appear like small clouds of dust. They may then 
be carried by the wind to a moist surface and there germinate at once 
by the formation of a hypha. This hypha becomes, as growth proceeds, 
the vegetative mycelium, thus completing the cycle of development. 
Whether these ascospores directly infect clover is not known, aside 
from the experimental work of Kehm (18) and Coleman (4). The 
former suspended mature fruit bodies over healthy plants and within 6 
to 8 days the mycelium was present within the leaf blades, the plants 
subsequently collapsed, and sclerotia were formed in due time. He did 
not determine the mode of entrance of the germ tubes, but regarded it as 
probable that they entered through the stomates. The latter reported 
that young clover plants only can be readily infected by ascospores, 
