Transpiration as a Factor in Crop Production. 
113 
Table 38. — Relation of water used by plants to atmospheric humidity. 
1912. Pop corn used. Grown in k-gallon potometers. Har- 
vested at silking stage. 
Drv 
TTiimid 
.1 -L U1111VL 
Ratio 
green- 
green- 
dry to 
house 
house 
humid 
11 U1111VA 
Number of potometers averaged 
10 
9 
Mean temperature 12 hours of day (F.) 
91 0 
90.0 
Mean temperature 12 hours of night (F.) . . 
81.0 
76.0 
Mean rel. humidity 12 h'rs of day (per cent) 
49.0 
71.0 
Mean rel. humidity 12 h'rs of night (per cent) 
67.0 
82.0 
Average dry weight per plant (grams) .... 
67.9 
71.9 
Average leaf-area per plant (square inches) 
543.0 
528.0 
Total water used per plant (kilograms) . . . 
24.279 
14.304 
Grams water used per gram dry weight 
(grams) 
357.30 
198.80 
100:56 
Grams water used per square inch leaf- 
area (grams) 
44.70 
27.11 
100:61 
Water evaporated per square inch free 
water surface (grams) 
125.50 
66.20 
100:53 
Table 39. — Relation of water used by corn plants to atmospheri ; 
humidity. Average of three tests in 1911 and 1912. 
Dry 
Humid 
Ratio 
green- 
green- 
dry to 
house 
house 
humid 
Number of potometers averaged 
20 
19 
Mean temperature 12 hours of day (F.) . . . 
91.0 
89.3 
Mean temperature 12 hours of night (F.) . . 
80.7 
75.7 
Mean rel. humidity 12 h'rs of day (per cent) 
45.0 
67.0 
Mean rel. humidity 12 h'rs of night (per cent) 
60.7 
78.7 
Average dry weight per plant (grams) .... 
84.2 
90.0 
Average leaf-area per plant (square inches) 
790.7 
775.7 
Total water used per plant (kilograms) . . . 
28.797 
18.803 
Water used per gram dry weight (grams) . . 
343.6 
200.2 
100:58 
Water used per square inch leaf-area 
(grams) 
38.95 
24.15 
100:62 
Water evaporated from 1 sq. in. free water 
surface (grams) 
128.33 
68.99 
100:54 
1 Compiled from Tables 36, 37, and 38. 
For a discussion of method used in compiling averages for two or more 
years see page 42. 
plants which had constantly been grown under those conditions. 
This relative transpiration rate was based on leaf -area. Leaf 
measurements were taken at the beginning and again at the end 
