58 
WATER REQUIREMENT OF PLANTS. 
exposed to the sun but otherwise similar ineveiy respect. The results, 
which are given in Table XL VII, show that the effect of the exposure 
of the pots to the sun is within the limits of other experimental errors. 
Table XLVII. — Water requirement of plants as influenced by the exposure of culture 
pots to the sun, according to Leather (1910, p. 142). 
Fertilizer. 
Water requirement. 
Crop. 
Pots pro- 
tected 
from sun. 
Pots ex- 
posed to 
sun. 
(Nitrate and phosphate . 
428 
630 
832 
1,014 
382 
\No fertilizer 
C06 
Wheat 
725 
\No fertilizer 
1,133 
Mean 
726 
712 
1 
CONCLUSIONS. 
From the data at hand no conclusion can be drawn concerning 
the effect of soil temperature on the water requirement. Leather's 
data indicate that the greater fluctuation in soil temperature accom- 
panying the exposure of the pots to the sun does not materially 
affect the water requirement. 
EFFECT OF CLIMATIC FACTORS ON THE WATER REQUIREMENT. 
EFFECT OF DIFFERENT ATMOSPHERIC CONDITIONS ON THE WATER 
REQUIREMENT. 
That atmospheric factors profoundly influence the water require- 
ment is evident from the data of numerous investigators. The 
effects of temperature, light, humidit}^, etc., will be discussed later. 
Here we wish to present the results which can be considered only 
as due to a difference in atmospheric conditions as a whole. 
fittbogen's experiments. 
Fittbogen (1874) published the results of measurements of the 
water requirement made in a plant house and in the open at the 
south side of the plant house. The culture method was the same 
as that used in 1873 (p. 12). The soil-moisture content was 50 to 
60 per cent of the moisture-holding capacity. The difference in 
the water requirement (Table XL VIII) of the plants grown inside 
and outside was 15 ± 6, which is without significance when the 
probable error is considered. The plants grown in the plant house 
were probably warmer, but were at the same time slightly shaded. 
On the other hand, the outside set received somewhat more solar 
radiation and was exposed to freer wind movement. It is impos- 
sible from data of this kind to draw conclusions as to the specific 
effect of temperature, light, or humidity upon the water require- 
ment, since none of these factors were comparable for the two series. 
285 
