A SERIOUS LETTUCE DISEASE. 
109 
Sclerotinia libertiana was grown upon lettuce agar, acidity -[-.55 
Fuller’s scale, and upon lettuce leaves at cool, room temperature, in¬ 
cubator temperature and in an open shaded window, all in ordinary 
diffused light except the culture in the incubator room which were in 
the dark. The results are shown in the following table. 
TABLE I.—SHOWING RELATION OF TEMPERATURE TO GROWTH. 
Figures Indicate Total Growth Recorded as Millimeters. 
Medium 
Condition 
Growth 
December 
1st 
3d 
4th 
5th 
6th 
7th 
8th 
10th 
11th 
12th 
13th 
Agar. . .. 
Window shaded. 
1 
5 
5 
5 
10 
15 
17 
23 
30 
35 
37 
Lettuce leaf.. 
Window shaded. 
0 
o 
•5 
5 
25 
30 
40 
60 
60 
70 
70 
Agar_ 
Cool room_ 
4 
13 
20 
n 40 
40 
47 
53 
70 
70 
78 
Lettuce leaf. 
Cool room . .. . 
20 
20 
20 
35 
50 
Agar . .. . 
Incubator room. 
4 
6 
6 
6 
6 
6 
6 
_ 
6 
6 
6 
Lettuce leaf.. 
Incubator room. 
4 
4 
4 
2 
/ 
It is clearly evident that the incubator temperature (approximately 
37 1-2 degrees) was unfavorable to the growth of the fungus. Growth 
stopped entirely after the first few millimeters and was not resumed, 
nor were any sclerotia formed. 
The room temperature, which was considerably warmer than the 
window temperature of December, was more favorable to growth, re¬ 
sulting in complete occupancy of the plate in 9 to 11 days. While 
growth was slower at the colder outdoor temperature it still continued 
vigorously and normally, leading eventually to complete occupancy 
of the plate. Sclerotia were formed upon the lettuce leaf at both room 
and outdoor temperatures. 
Experiment 48, March 12, 1908. To determine more accurately the 
optimum growth temperature in agar, cultures were made in this me¬ 
dium and placed in an optimum temperature apparatus.* 
The work was done in quadruplicate and care was taken to have all 
cultures as nearly as possible parallel as to moisture, quantity and 
quality of inoculum and all factors except temperature. The results 
are expressed in table II. 
It is seen that growth was markedly less in the two warmer com¬ 
partments (29 and 36-39 degrees). ISTo growth at all occurred in the 
warmest compartment and no sclerotia formed in either of these com¬ 
partments. In the compartment of lowest temperature (13-18 degrees) 
growth was also much retarded but it still continued, leading to com¬ 
plete occupancy of the plate in twelve days and to sclerotial forma¬ 
tion in thirteen days. 
*An incubator with six compartments, giving a considerable range of temperatures. 
