30 BULLETIN 759, U. S. DEPARTMENT OF AGRICULTURE. 
it does not seem unlikely that this fungus winters in the same way 
that has been demonstrated for its close relative on alfalfa. 
METHOD OF DISTRIBUTION. 
SUGGESTIONS FOUND IN THE LITERATURE. 
Since the method of overwintering of these fungi has been traced, - 
it is now possible to see their entire annual cycle in a field in which 
they have once been introduced. But thus far no information has 
been gained which serves to indicate how they are conveyed into 
new localities in which the host plants are grown for the first time. 
This phase of the problem is of special importance in connection 
with the alfalfa leaf-spot. A large amount of recorded experience 
indicates that this disease appears wherever alfalfa is grown, re- 
gardless of environment. A knowledge of the source of infection in 
these new localities might suggest feasible control measures. 
Scattered through the various discussions of the alfalfa leaf-spot 
are found four suggestions that have been put forth to explain the 
constant appearance of Pseudopeziza on alfalfa in newly seeded 
fields: It is suggested (1) that the fungus is carried with the seed, 
(2) that it is conveyed in soil that is used to inoculate the new field 
with the bacteria producing nodules on the roots, (8) that the fungus 
spores are generally distributed in the air, and (4) that other host 
plants near by furnish the source of infection. Since none of these 
suggestions are supported by carefully controlled experimental evi- 
dence, they must be subjected to examination before they are used as 
working hypotheses in experimental work. 
The first suggestion, that the fungus is carried with the seed, de- 
serves careful attention. This might happen in three ways. Spores 
might adhere to the seed coat, spores or fragments of the fungus 
might accompany the seed, and living mycelium of the fungus might 
occur within the seed. When the conditions under which seed is 
produced are examined it is found that the fungus spores are prac- 
~ tically all discharged and blown away before the seed is thrashed, 
thus making it highly improbable that spores are attached to the seed 
except as a rare occurrence. Commercial seed is so well cleaned that 
there appears to be small chance that fragments of the fungus are 
often conveyed with the seed. 
The possibility that fragments of the fungus as well as the spores 
may be carried with the seed appears unlikely in the case of most 
commercial seed. Débris consisting of plant parts is so light in com- 
parison with the seed that it is easily removed. Nevertheless, Ivy 
Massee (1914) states that she has examined commercial seed and 
1On April 6, 1919, apothecia of Pseudopeziza trifoliti were found abundantly on living 
overwintered clover leaves at Madison, Wis., showing clearly that young leaves infected 
late in the autumn under favorable conditions may carry the fungus over winter. 
