1916] 
GILMAN—CABBAGE YELLOWS 51 
Ascomycetes.—In the Ascomycetes but little has been done 
on the temperature relations of the parasitie forms. In Ohio, 
Selby (799, '04) observed that the leaf curl of the peach, 
caused by Exoascus deformans, was favored in its occurrence 
by relatively low temperatures in April, May, and June, the 
weather in April having the greatest influence. These conclu- 
sions were based on observations made over a period of ten 
years, 1893-1903. Duggar (709) showed that the same was 
true in New York. Pierce ('00) found that similar conditions 
brought about the attack in California, and attributed the vir- 
ulenee of the attack to the harmful aetion the adverse weather 
had on the host, eausing it to be weakened. He also noted 
that hot dry weather would check an attack which had al- 
ready started. 
That Sclerotinia Panacis, the cause of black rot of the gin- 
seng root, was favored by eold weather was shown by Van 
Hook (’04). This author found that this disease developed 
only in the winter, also a time when the roots were in a dor- 
mant state. 
Germination of the spores of Sphaerotheca Нитий has been 
shown by Salmon (’00) to be increased if the spores were 
previously exposed to cold, especially freezing, temperatures. 
The germination, however, took place only when the higher 
temperatures were restored. Sajó (701) observed that Oidium 
Tuckeri on grapes was favored by subnormal temperature 
and moisture. 
Probably one of the first observations of scientific value on 
the relation of temperature to a particular plant disease was 
that made on the black rot of grapes by Buchanan in 1850. 
As is reported by Viala ('87), Buchanan noticed that this dis- 
ease was worse after a period of hot weather. Viala also 
made observations on this relation and found that in hot 
weather (maximum 35-37^C. minimum 18-20°С.) there 
was a bad epidemie of the trouble. When the temperature 
fell the disease became checked. His observations covered 
a period of two years. Later Edson (203), making observa- 
tions in North Carolina, came to similar conclusions. 
