1916] 
GILMAN—CABBAGE YELLOWS 49 
edly an important faetor in the case of diseases caused by 
the fungi, there has been insufficient work on the question 
to warrant more than a general discussion of the subject. 
In spite of this lack of correlated facts on the relation of 
temperature to plant disease, there are many isolated notes 
seattered through plant pathological literature, and an at- 
tempt has been made to bring them together at this time. 
In order to put them in the best shape for comparison, one 
with another, it was thought well to arrange them according 
to the natural grouping of the parasites upon which the ob- 
servations were made. 
Schizomycetes.—'The diseases caused by bacteria may be 
placed first. Halsted (’98) pointed out that the summer of 
1894, which was excessively hot in New Jersey, was charac- 
terized by an outbreak of fire blight due to Bacillus amylovo- 
rus. Whetzel (’06), from evidence in New York, confirmed 
this relation but considered that moisture was the more im- 
portant factor limiting the outbreak of an effective epidemic 
of this disease. 
Schuster (712), working with the bacterial rots of potato, 
showed that at high temperatures (35°C.) saprophytic spe- 
cies, as, for example, Bacillus fluorescens, might become para- 
sitie on potato tubers, causing soft rot. 
Smith (214) noted that in rapidly growing shoots of sus- 
ceptible hosts the incubation period of Bacillus Solanacearum 
is shortened in very hot wet weather from 8-10 days to 2-3 
days. He attributes the decrease to a difference in suscepti- 
bility in the host rather than to a change in the virulence of the 
invading organism. 
Phycomqycetes.—Perhaps more work has been done on the 
temperature relations of the Phycomycetes than of any other 
group of fungi, but the major part of these studies has been 
with its relation to spore germination. 
Atkinson (795) found that high temperature was a contrib- 
uting factor to damping off by Pythium deBaryanum, which 
view is corroborated by Johnson (714) working at Wisconsin, 
although neither of these authors show any experimental evi- 
dence to support their opinion. 
4 
