1917] 
FREIBERG—MOSAIC DISEASES 195 
extract is of course unknown, but this is another possibility. 
Although no infections could be attributed to inoculations 
with the cucumber extract, the disease was, during the season, 
contracted by plants of pumpkin, squash, citron, cassaba, 
and two varieties of cucumbers. Some observations in this 
connection are also reported by Doolittle (716). 
TEMPERATURE AND MOISTURE RELATIONS 
Although it is occasionally stated in the literature on 
mosaic diseases that high temperature favors the disease, 
there are, nevertheless, no quantitative data nor detailed ex- 
periments to substantiate this view. An interesting observa- 
tion in this connection was made during the summer of 1916. 
Tomato plants which had been transplanted to the plot grew 
normally until the latter part of July when, due to drought 
and high temperature, they discontinued growing but other- 
wise appeared perfectly normal. These climatic conditions 
continued until the middle of August when several rains oc- 
curred which were followed, though not immediately, by com- 
paratively cool weather. It was during these 10 days of cool 
weather, from August 23 to about September 2, that mosaic 
began to show on the tomato plants. During this period 
growth was resumed and all new shoots and buds were notice- 
ably affected. 
Following this comparatively cold period, there was an- 
other hot spell during which there not only was a high de- 
parture from the normal but the maximum for the individual 
days was higher, reaching 94° F. During this second, though 
relatively short, warm period accompanied by reduced pre- 
cipitation growth ceased and the mosaic began to disappear. 
The chlorotic areas became darker, and the small amount of 
expansion which did take place in the leaves of the new shoots 
was not accompanied by malformations. Had it not been for 
the fact that the plants were under constant observation, the 
periodic occurrence of mosaic would have escaped notice en- 
tirely. No records pertaining to temperature and moisture 
were taken on the plot, but the following tables from the U. S. 
Department of Agriculture Weather Report present the 
