Transpiration as a Factor in Crop Production. 105 
VARIATION IN WEEKLY TRANSPIRATION IN RELATION TO CLIMATIC FACTORS. 
In 1914 a complete weekly record of transpiration and the 
climatic factors were obtained thruout the entire growing season. 
The results are given in Table 31 and Chart XVI. 
The weekly water requirement gradually increases early in 
the season with the growth of the plant, regardless of the weather 
conditions. Late in the season the water requirement decreases, 
due to the ripening of the plant and consequent reduction in the 
amount of transpiring leaf surface. As the plant ripens, the 
leaves fail to function, become dry, and consequently have no 
moisture to be evaporated. In 1914, the leaf-area of the plants 
continued to increase until about July 8 and remained fairly 
constant until about August 15, when it gradually became reduced 
by the maturing of the plants. With a given variety, the dates 
of this cycle of development vary a few weeks in different years, 
according to climatic conditions. The season of 1914 was 
especially early. 
Table 31. — Weekly summary of transpiration from corn plants 
and weather factors thruout the growing season. (Average of 21+ 
plants.) 19l\. 
Mean 
Water 
hourly 
Mean 
Av. hourly 
Week 
Week 
transpired 
tempera- 
relative 
wind velocity 
Per cent of 
No. 
ending 
per plant. 
ture. 
humidity 
10 ft. above 
possible 
7 p. m. 
(Av. 24 
(7 a. m.- 
(7 a. m.- 
ground. 
sunshine 
plants) 
7 p. m.) 
7 p. m.) 
(7 a. m.-7 p. m.) 
Kilograms 
Degrees F. 
Per cent 
Miles 
Per cent 
(1) 
(2) 
(3) 
(4) 
(5) 
(6) 
(7) 
1 
June 1 
.141 
77.6 
74.6 
8.5 
67.3 
2 
7 
.412 
79.6 
77.2 
13.8 
67.1 
3 
" 14 
1.498 
76.6 
82.4 
7.4 
52.6 
4 
" 21 
6.430 
78.0 
75.3 
7.5 
61.3 
5 
" 28 
8.421 
80.9 
64.1 
10.7 
84.3 
6 
July 5 
" 12 
10.784 
77.3 
65.4 
7.6 
70.3 
7 
20.667 
85.7 
62.2 
8.6 
85.0 
8 
" 19 
20.444 
83.1 
62.3 
8.8 
74.4 
9 
" 26 
20.202 
86.2 
64.5 
7.7 
70.4 
10 
Aug. 2 
9 
15.538 
82.3 
67.9 
7.9 
54.0 
11 
21.214 
86.1 
57.7 
7.6 
87.6 
12 
" 16 
14.777 
80.0 
59.7 
8.9 
79.0 
13 
„ 23 
14.381 
85.0 
66.0 
7.6 
66.6 
14 
" 30 
5.882 
73.2 
67.1 
6.2 
51.5 
15 
Sept. 6 
7.030 
79.0 
55.1 
7.1 
78.0 
