4 BULLETIN 1288, U. S. DEPARTMENT OF AGRICULTURE 
It is evident from the results presented in Table 1 that the tomato 
leaf-spot fungus is able to grow and sporulate on a number of 
dead weed and crop plants. Its abundant sporulation on corn- 
stalks agrees with its behavior on corn meal and corn-meal agar, 
on which, with the possible exception of potato agar, it fruits better 
in pure culture than on any other medium used. It would be inter- 
esting to know whether it also grows and fruits abundantly on 
dead potato vines. Apparently this fungus will not grow on rough 
pigweed and lambs-quarters. In fact, none of the tomato parasites 
tried grew on lambs-quarters. From the results of these experi- 
ments it would appear that the fungus can live from year to year 
on dead cornstalks, weeds, and pieces of crop plants not completely 
covered by soil. 
Fig. 3. — Outline map of the United States, showing the relation of temperature to the 
distribution of tomato leaf-spot. The isotherms and temperature figures indicate the 
average monthly temperature for July ; other figures show the average percentages of 
tomato crops destroyed by leaf-spot from 1918 to 1921 
EFFECT OF SOIL ON THE VIABILITY OF THE FUNGUS 
As weeds and crop remains are largely covered by soil in plow- 
ing and most fungi do not grow in soil, experiments were made to 
determine the effect of soil on the viability of the leaf-spot fungus. 
Dead plant material was tubed and sterilized, as in the previous 
experiments, inoculated with Septoria lycopersici, and after 3 to 18 
days thoroughly covered with soil. The tubes were then plugged 
with cotton wool, packed in cans, and exposed during the winter to 
outdoor temperatures. Those kept in the laboratory 3 days were not 
examined before the addition of soil, as Septoria grows very slowly 
and the period was too short for visible growth on most of this 
material. As the same kinds of media and the same tubes of inocu- 
lation material were used in both the 3-day and 18-day sets and 
growth was evident in the latter, it no doubt had started in the 
former before the addition of the soil. The effects of the soil on 
the viability of the fungus, as determined by microscopic examina- 
