6 
PERONOSPOREiE AND RAIN-EALL. 
By Byron D. Halsted. 
The chief point in this paper is to contrast the prevalence of the 
Peronosporece during the past year with the quite general absence of 
them the two previous years. It will be necessary to state the leading 
difference in the rain-fall of the last two years, and as this is the only 
apparent element of variation, except in so far as this modifies other 
meteorological conditions, it is only natural to attribute the variations 
in amount of mildew largely to the difference in the rain-fall. 
The year 1887 was an exceedingly dry one and the last growing sea¬ 
son has been not far from the average one in moisture. In 1887, accord¬ 
ing to the weather record kept at the college (Ames, Iowa) and kindly 
furnished me by Professor Osborn, the showers in time and amount were 
as follows: 
Inches. 
Mar. 5..10 
Mar. 27.-.56 
Apr. 23. 1.26 
Apr. 26.02 
May 14. 16 
May 22.08 
May 29. 15 
June 6.02 
June 11.20 
June 12.43 
June 13.,. 1.16 
June 20. 23 
July 13.45 
July 16.02 
Inches. 
July 17.02 
July 18.30 
July 19. 1.45 
July 22.13 
July 30.41 
Aug. 5.23 
Aug. 9..*..11 
Aug. 10.08 
Aug. 18.09 
Aug. 20. 40 
Aug. 21. .08 
Aug. 26.10 
Aug. 30.08 
By month this gives ior— 
Inches. 
March.66 
April... 1.28 
May. 1. 39 
Inches. 
June . 2.04 
July. . .. 2.78 
August ... 1.17 
This is an average of only 1.39 inches per mouth and a total of 8.32 
for that half of the year when rain is most essential for the existence and 
growth of vegetation. This prolonged drought was made more intense 
by the preceding dry year. It was in fact the second of two compara¬ 
tively rainless seasons. September opened with refreshing showers, and 
by the close of the mouth the rain fall amounted to nearly 10 inches (9.77). 
For six months in 1888 the rainy days were as given below: 
Inches. 
Inches. 
Apr. 26-29 . 1.22 
May 3-4. 1.51 
May 7-9. 1.47 
May 27-28.. 1.11 
May, scattering (3).46 
June 1.38 
June 12. 17 
June 20-21. 1. 19 
June 27. 66 
July 4-5. 
J uly 16. 
July, scattering (3). 
Aug. 5-6. 
Aug. 10. 
Aug. 14-15. 
Aug. 28. 
Sept., scattering (4) 
1.86 
1.73 
.58 
.37 
.65 
1.38 
.14 
.16 
