LEAF-SPOT OF ALFALFA AND RED CLOVER. 31 
found the fungus present. This can hardly be a common occurrence 
in America. 
The possibility that the fungus may be present in the seed as 
mycelium is open to the objection that this involves a larger or 
smaller amount of systemic infection, both of the plant producing 
the seed and of the seedling. No evidence of such a relation of these 
fungi to their host plants has been found, and therefore this method 
appears highly improbable. 
The second suggestion, that the fungus is conveyed with plant 
debris that accompanies soil which is transported to new fields, may 
and probably does account for a small amount of the distribution of 
the fungus. But owing to the restricted extent of this practice, this 
method must be of minor importance. 
The third hypothesis, that spores of Pseudopeziza are generally 
distributed in the air, has been advanced several times in a vague 
way either in a discussion of conditions where large areas of dis- 
eased alfalfa were growing at no great distance or with an implied 
belief that some other host plant in the vicinity was the source from 
which this general infection arose. In the vicinity of areas of dis- 
eased alfalfa it is highly probable that spores are borne to a consid- 
erable distance by wind, but it is not often that the spores are pro- 
duced so abundantly that they are likely to be conveyed great 
distances in large numbers. 
The final hypothesis, that other hosts provide the source of infec- 
tion, has been rendered less probable by results already presented. 
The only common hosts that can be considered are red clover and yel- 
low trefoil (Medicago lupulina). Pseudopeziza on red clover appears 
to be a distinct species from that on alfalfa, and no evidence has 
been obtained indicating that the fungus on yellow trefoil can cross 
to that host. 
Thus, -a. summary of the available evidence does not point clearly 
to any of these suggestions as the one most likely to contain the 
truth. However, the suggestion that the fungus is carried with the 
seed affords most opportunity for experimental study and, if found 
true, affords the greatest opportunity for the application of control 
measures. The following experiments in seed sterilization were car- 
ried out. 
EXPERIMENTAL METHODS AND RESULTS. 
Laboratory experiments. — If the fungus spores are carried adherent 
to the seed they must inevitably germinate upon the seed coat and 
produce apothecia there, if at all. In order to determine to what 
extent the fungus is capable of developing upon the seed coat, spores 
were discharged upon seeds sterilized with formaldehyde. The seeds 
were then germinated upon agar in test tubes. After a time minute 
