EFFECT OF CLIMATIC FACTORS ON WATER REQUIREMENT. 63 
PFEITFER. BLAXCK. AXD FLUGEL*S EXPERIMENTS. 
PfeifTer. Blanck. and Fliigel (1912) obtained a slight increase in the 
water requirement of oats, due to shade. Unfortunately, however, no 
idea is given of the light reduction resulting from the use of the shade. 
Then results are given in Table XIII (p. 24). The difference in the 
water requirement of the shaded series and the series in full light was 
20 = 3. which corresponds to an increase of about 5 per cent due to 
shading. 
CONCLUSIONS. 
The intensity of the sunlight or the extent to which it was reduced 
by the various shades used is not stated hi any of the above investi- 
gations, so that it is not possible to draw specific conclusions from the 
data here presented. All of these data, however, indicate that shad- 
ing produces an increase in the water requirement. It seems probable 
that hi these experiments the shade was so dense as to reduce photo- 
synthesis. This would in turn decrease the rate of growth and so 
increase the water requirement. 
EFFECT OF AIPv HUMIDITY OX THE WATER REQUIREMEXT. 
sorauer's experiment^. 
Sorauer (1880) investigated the effect of humidity on the water 
requirement by growing a number of woody plants in moist air and 
in dry air. (Table LIII.) The water requirement in moist air aver- 
aged about. SO per cent of the water requirement in dry air. 
Table LIII. — Effect of dry and moist air on the voter requ f woody plants, 
according to Sorauer 1880, p. 
Plants. 
Moist air. Drv air. 
Duration. Xumber of Water re- Number of Water re- 
determi- quire- determi- quire- 
nations, ment. nations. ment. 
Days. 
Pyrus communis 
Pyrus malus 
Vitis vinifera 
Ailanthus glandulosa 
Robinia pseudoacacia 
Mean. 
39 
1 
1 
3o3 
39 
3 
146-3 
2 
. J±27 
39 
2 
113 -s 
2 
39 
1 
497 
1 
467 
39 
1 
1 
441 
274 
343 
HEIXRICH S EXPERIMENTS. 
Heinrich (1894) grew oats hi damp air and in air dried by calcium 
chlorid. (Table LIT.) The plants were grown in glass pots, only one 
pot being used in each experiment. The relative humidity of the air 
is not given in either experiment. The results are very striking, the 
water requirement of the plants grown in dry ah- being over five times 
that of the plants grown in moist air. 
285 
