354 OHIO EXPERIMENT STATION: BULLETIN 214 
Stress has been laid upon the downy mildew of potato and 
cucumber respectively. It must not be inferred that other diseases 
do not offer like contrasts between dry, hot seasons and those of 
heavy precipitation and low temperatures accompanied by relatively 
high atmospheric humidity. Mention has already been made of the 
greater prevalence of the shot-hole disease of the plum and leaf-spot 
of cherry, Cylindrosporium padi, in rainy seasons over drier ones. 
The same facts will apply with respect to practically all external 
parasites of plants as in the scab fungus on the apple, the rot of 
plum, cherry and peach, and to the countless number of foliage 
diseases with which we deal from year to year. 
Contrasting with the potato Phytophthora is the allied disease 
of curcurbits, the downy mildew, lasmopara cubensis, which 
appears to flourish during our hot seasons and to disappear during 
the cool ones where grouped as above described. The writer has 
suggested that this Plasmopara does not survive in our climate but 
is carried northward each year by its conidia alone; the extent of 
spread will thus be limited by the length of period favorable to it. 
This period must be one of relatively high temperatures since this 
parasite is more widely distributed near the tropics. All these 
instances only make more clear the intricacies of the mutual 
adaptations of parasite and host which have resulted from the long 
periods in which these dwell together. 
MEAN SUMMER TEMPERATURES AND RAINFALL IN OHIO, 1883-1909 
Mean temperatures degrees Fahr. Mean Rainfall, inches 
Year Three 3 Mos. 
May June_| July -|August|/months}| May June | July |August] Total 
Mean inches 
69. 72.1 68.2 69.8 5.72 4.25 -16 .88 | 10.29 
1.1 71. 70.8 71.1 3.87 2.96 83 45 8.24 
7.1 vin 68.9 70.4 3.97 34 20 .33 | 13.87 
7. 72. 70.9 70.1 23 53 88 .62 | 10.03 
L. 7. 77.9 75.6 87 85 16 .39 8.40 
0.4 72. 70.4 71.0 77 41 4.40 16 | 12.97 
66. 72. 69.1 69.4 i 4.13 25 .50 9.88 
3. 2B. 68.8 VL? 5.52 4.50 <f -70 | 11.19 
i, 69. 70. 70.0 -20 . 82 82 .O7 | 11.71 
3. 2B. 71. 72.3 6.32 5.61 .80 -99 | 12.40 
0. “4 70. 71.9 4.97 34 49 17 8.00 
i. . 71. 72.3 4.00 65 56 67 5.88 
2. Vis 2. 72.4 1.80 47 2.00 96 7.43 
69. 73.2 71. 71.5 2.67 4.81 8.11 38 6.30 
68. 1.5 69.4 71.0 3.93 2.85 4.65 -72 | 10.22 
71. 76. 73.5 73.5 4.10 2.96 3.98 4.50 | 11.34 
71. 74.1 73. 73.1 4.32 2.96 4.18 82 8.96 
69.8 74.1 76. 73.4 2.40 2.99 4.62 .68 | 11.29 
70.9 7.1 2B. 74.0 69 4.38 2.73 .82 | 10.43 
66.9 74, 67.4 69.0 09 7.48 4.69 .67 | 13.84 
64.4 i 70.7 69.3 82 3.97 3.67 -20 | 10.84 
4 71.4 68.8 69.5 ve 2.88 4.13 2.74 9.7 
69.2 73. 71. 71.3 63 4.72 3.93 4.46 | 13.11 
69.8 74. 72.2 17 3.41 5.14 TT | 13.32 
65.6 72 69. 69.2 ¥| 4.57 5.36 48 | 12.41 
69.2 3 71. 71.4 4.72 2.52 4.08 .59 9.1 
70.1 | *69.6 | *70. 70.0 4.72 5.86 | *4.05 | *5.21 6.04 
Ohio, ’83-’09 ...... 60.6 69.6 73.44 | 71.3 71.4 3.88 3.93 4.08 3.12 | 10.82 
* Records Wooster only, not included in other than 1909 averages. 
