LEAF-SPOT OF ALFALFA AND RED CLOVER. 27 
LIFE HISTORY OF THE CAUSAL ORGANISM IN RELATION TO 
THE HOST PLANTS. 
AMERICAN STUDIES BEARING ON LIFE HISTORY. 
The great economic importance of the alfalfa crop in America 
has inspired the small amount of work which has been done upon 
this disease with a point of view quite different from that shown in 
the European studies already reviewed. Life history has been studied 
with a view to the possible control of the disease. 
The first work was done by Chester (1891) at the Delaware 
Agricultural Experiment Station. In 1889 twenty plats of alfalfa 
were seeded in different parts of Delaware, with seed from the 
same source. The disease appeared on all of these plats at about the 
sixth week after planting. The plat under closest observation at 
Newark showed a yellowing of the leaves accompanied by black spots 
before Pseudopeziza was found fruiting on some of the dark spots. 
Evidently some other disease was associated with Pseudopeziza, 
Chester concludes from this experiment that the disease is carried 
by the seed and next tries a method of disinfecting the seed in order 
to prevent such conveyance. Seed was treated with copper sulphate 
and planted in heat-sterilized soil in cans. The diseases appeared 
on all the plants from these cans. Therefore, Chester concludes that 
the source of the disease must be a general atmospheric infection. 
Unfortunately, in none of his experiments does he give any details 
regarding the proximity of his plats or plants in cans of sterile soil 
to alfalfa which was infected with the leaf -spot and- which might 
have been a source of wind-borne spores. 
The only other attempt to study the disease which has been re- 
ported was made by Coombs (1897a) in Iowa. On August 20 alfalfa 
seedlings 3 weeks old grown under bell jars were treated as follows: 
One was left as control, one sprayed with germinating Pseudopeziza 
spores, and one sprinkled with powdered diseased leaves showing 
disease. Next, plants growing in the field were cut back, and after 
the debris was removed, the roots were protected by large bell jars. 
In the next six weeks the plants outside the bell jars became diseased, 
while those inside were healthy. However, when the jars were re- 
moved the plants immediately became diseased. As a result of this 
work Coombs concludes that two things are established: (1) That 
plants are infected by spores from the air and (2) that the disease is 
strictly local and not systemic. 
It will be seen at once that these conclusions are based on a very 
small amount of experimental evidence. Such important factors as 
the high temperature and absence of clew or rainfall inside the bell 
jars do not appear to have been considered as possible conditions 
