Oct. 23,1916 Daily Transpiration during Normal Growth Period 181 
During the August transpiration period in 1914 (Table X) the alfalfas 
showed an hourly transpiration loss near midday of from 3.6 to 5.6 gm. 
per gram of dry matter. * In other words, during the last third of the 
growth period the alfalfa crops lost during each midday hour an amount 
of water ranging from 3.6 to 5.6 times the dry weight of the crop. 
The conditions in 1915, as has already been mentioned, were less 
severe than in 1914. The evaporation during the July maximum trans¬ 
piration period in 1915 was only 60 per cent of that during the corre¬ 
sponding period in 1914. The transpiration loss of the small grains 
each hour during midday was approximately equal to the dry weight 
of the crop (Table XI). The transpiration loss of the flax varieties was 
nearly twice as great. 
During the second transpiration period considered in 1915 (Table XII), 
the midday loss was still further reduced, being approximately one-half 
that observed in 1914. 
DAILY LOSS OF WATER IN ACRE-INCHES PER TON OF DRY MATTER HAR¬ 
VESTED PER ACRE 
From a practical standpoint it is desirable to express the daily trans¬ 
piration loss in terms of acre-inches of water per ton of dry matter pro¬ 
duced per acre. This is given in the last column of Tables IX to XII. 
A wheat crop yielding a ton of dry matter (grain and straw combined) 
would thrash approximately 12 bushels of wheat. Such a crop at 
Akron in 1914 would have used approximately 0.13 acre-inch of water 
each day during its maximum transpiration period. Millet, com, 
and sorghum required approximately one-half this amount per ton of 
dry matter, while the alfalfas during their maximum transpiration 
period required the equivalent of a rainfall of from 0.3 to 0.5 inch per 
day per ton of dry matter produced per acre. 
LOSS OF WATER DURING MAXIMUM TRANSPIRATION PERIOD PER SQUARE 
METER OF PLANT SURFACE 
The surface area of the plant tissues of the different crops included in 
the transpiration measurements was determined from a selected sample 
of the plants in one pot of each set. The ratio of the portion selected to 
the whole crop was found by comparing the green weight of the sample 
(taken immediately after cutting) with the green weight of the whole 
crop. The area of the selected portion was determined by one of the 
following methods: (1) By direct measurement of the length and 
breadth (or diameter) of the leaves or stems; (2) by pasting the leaf and 
flower parts on surgeon's tape and determining the area by measure¬ 
ments; (3) by prints of the pasted leaves on squared photographic 
paper, the area being determined either by direct counts of the squares 
on the paper or by a planimeter. From the total area of the sample and 
