228 
Journal of Agricultural Research 
Vol. VIII, No. 6 
TEMPERATURE TESTS 
Of 8o transfers of two isolations of the fungus to corn-meal-agar slants 
40 were placed at once in a io-compartment refrigerator with tempera¬ 
tures ranging from 2 0 to 19 0 C. The other half were placed in the com¬ 
partments the following day, after the conidia had germinated. Where 
germination had occurred before placing cultures in the refrigerator, a 
very slight growth took place at 2 0 , but no perceptible growth occurred 
where transfers were held from the start at this temperature. Slight 
mycelial growth took place at 4 0 to 5 0 in all tubes with increase in 
rapidity following a rise in temperature. Development of conidia began 
at 8° to 9 0 and increased in rapidity up to the highest temperature 
tested. Sclerotia began to develop at 8° to 9 0 , increased in numbers up 
to 14 0 to 15 0 , and declined in numbers up to 19 0 to 20°, where but few 
were formed. All cultures held at the lower temperatures developed 
rapidly when later placed at 18 0 to 20°. These observations covered a 
period of five weeks. 
HOST-PARASITE RELATION 
Numerous microscope sections have been made of naturally infected 
leaves and also of artificially infected leaves at periods of time vary¬ 
ing from a few hours to several days after inoculation. Study has 
also been made of portions of leaves killed, bleached, and stained without 
sectioning at 18, 24, 48, and 72 hours after sowing the conidia on the 
upper surface, as in the inoculation experiments previously detailed. 
In the older spots the tissues are seen to have more or less completely 
collapsed and fungus mycelia are found ramifying both between and 
within the decaying cells, together with coccoid and rod-shaped bacteria 
and various protozoa, a condition to be expected in a decaying mass of 
tissue floating on a watery medium. In the case of leaves studied 
without sectioning, germination of the conidia has been noted on the 
leaf surfaces at 18 and 24 hours after inoculation, and in several cases 
at 24 to 48 hours the germ tubes were seen entering a stomatal open¬ 
ing. By focusing down the continuation of the hyphae was also seen 
below the guard cells and epidermal cells in the substomatal cavity. 
Furthermore sections of leaf spots at three to four days after inocu¬ 
lation have shown in numerous instances the hyphae entering the stomatal 
opening and branching out in the chamber below (PI. 70, B, C). In 
slightly older spots the pale brownish hyphae have repeatedly been seen 
ramifying between the cells of the spongy parenchyma and through the 
large air chambers, as also between the cells of the palisade tissue. But, 
except in old decayed and water-logged spots, hyphae have not been 
seen within the cells. 
It is clear that infection may and does occur through the stomata, 
but this is very evidently not the only method. Infection occurs, 
