122 
Journal of Agricultural Research 
Vol. XXIV, No. a 
RESUI.TS 
Amount of Transpiration Compared with 1917 
The first point to be noted in Table VII is that the amount of transpira¬ 
tion in 1920 was very much less than in 1917. 
On the basis of mean green weight it was 42.4 gm. in 1920, as compared 
with 123.0 in 1917. On the basis of leaf exposure it was 8.81 gm. in 1920, 
as compared with 20.6 in 1917. For leaf area we have no data in 1920. It 
is evident, however, that, considering the amount of water used in rela¬ 
tion to size of trees, the transpiration was only one-third to two-fifths 
as great in 1920 as in 1917. This may be accounted for— 
1. By a season of only about 147 days for the average tree in 1920, as 
compared with 203 days in 1917. 
2. By reason of mudd lower air temperatures in 1920. 
3. By reason of considerably less sunshine in 1920, but especially the 
lack in June, when the driest atmosphere usually prevails. The following 
data for whole months give the sunshine in recorded minutes: 
May. 
June. 
July. 
•August. 
September. 
Total 
1917. 
1920. 
8, 
622 
9 ) 
598 
15, 
807 
8 , 
903 
12, 
932 
II, 
310 
10, 
496 
II, 
704 
10, 
/ 
II, 
695 
58 > 
299 
53 » 
210 
It is also probable that on account of the arrangement of the room the 
trees received a smaller percentage of the total sunshine in 1920. 
4. The water of the soil was less readily obtainable in 1920. 
TABrie VII .—Actual water losses and transpiration in relation to size and growth in igzo 
Spedes. 
Yellow pine. 
Douglas fir. 
Pot No. 
Transpiration; 
May II to 31... 
Jime. 
July. 
August. 
September. 
October (to day indicated).. 
Total for season. 
Correction, direct evaporation. 
Net transpiration.. 
Transpiration: 
Grams per gram weight ac¬ 
cretion— 
Green... 
Dry.. 
Grams per gram mean green 
weight. 
Grams per square centi¬ 
meter leaf exposure. 
23 
I 
x 8 
IS 
*7 
XO 
7 
SI -5 
52.8 
35-6 
66.2 
83.0 
X08.9 
XX2. 0 
ZO9. 0 
X12.0 
102. 7 
X44.6 
XIX. 4 
X 22 9 
134-0 
132-4 
163. X 
236.4 
22)0. 0 
1 X 7-6 
163.6 
X 49-0 
x 6 i. 3 
236. 8 
338.2 
492. 7 
130.3 
180.0 
177.0 
151-4 
292.8 
313-0 
S09.4 
130.9 
190.3 
181.8 
(7) 
( 8 ) 
( 8 ) 
( 7 ) 
( 8 ) 
(5) 
(6) 
31-6 
80. 5 
73 - 7 
105.9 
47-8 
32.x 
39-7 
637-1 
939-0 
1 , 099-6 
1,598.8 
621.0 
796.8 
793 - 5 
79*4 
79.6 
79-6 
79-4 
79.6 
77-7 
79-0 
557-7 
859-4 
X, 020 . 0 
1,519.4 
541-4 
719-1 
714-S 
71S 
23X 
X85 
151 
SOI 
345 
564 
592 
6X5 
514 
302 
506 
992 
26. X 
41. 8 
56.8 
67.3 
19-1 
2 X. 6 
32. X 
6-5 
XO. X 
9.5 
14. 2 
3.8 
S-i 
S-o 
