334 
AMERICAN JOURNAL OF BOTANY 
[Vol. 9 
less extent the light intensity. The shrub zone was so dense in many places 
that passage through it was almost impossible; such places did not occur 
in the bur-oak forest. The evaporation was lower in the low prairie than 
in the high prairie because it was less exposed to the sun and wind, it was 
in the shade later in the morning and earlier in the evening, and it retained 
the dew longer. 
2. Soil Moisture 
Soil moisture readings were taken eight times from May i8 to July 19 
at depths from o to 10 cm. and 10 to 30 cm. in each of the six stations where 
the atmometers were operated. These readings, with wilting coefificients 
for three of the stations, are given in table 2. 
At both depths, o-io cm. and 10-30 cm., the readings show with striking 
regularity that the high prairie had the lowest soil moisture, this increasing 
in the stations in the following order: low prairie, bur-oak forest, shrubs 
and red oak-hickory forest. Water was unavailable for plant growth in the 
Table 2. Total Water Content of the Soil at Depths of o-io cm. and 10-30 cm. in Various 
Stations at Peru, Nebraska, igi/ 
Wilting 
May 
May 
June 
June 
June 
July 
July 
July 
Aver- 
Coeffi- 
Station 
18 
26 
2 
12 
19 
4 
15 
29 
age 
cient 
O-IO cm. 
% 
% 
% 
% 
% 
% 
% 
% 
% 
% 
High prairie 
8.9 
23.3 
26.6 
7-3 
12.5 
15-8 
54 
14.5 
13.0 
Low prairie 
12.8 
15-5 
28.4 
18.7 
9.0 
15.0 
18.4 
6.6 
15-5 
Dogwood-bur oak 
16.8 
shrub 
19.8 
28.3 
32.9 
25-9 
22.6 
24.0 
11.4 
22.7 
Prickly ash-dog- 
wood shrub .... 
23.1 
32.1 
33-9 
29.9 
18.7 
23-5 
25-9 
14.5 
25.2 
Red oak-hickory 
forest 
32.7 
37-1 
38.5 
34-0 
27.9 
33-0 
30-9 
15-7 
31.2 
15-5 
Bur-oak forest . . . 
16.9 
27.1 
31.0 
24.0 
16.2 
21.9 
19.6 
9.8 
20.8 
15.2 
10-3C cm. 
% 
"~%~ 
% 
% 
% 
% 
% 
% 
% 
% 
High prairie 
13.3 
19.8 
23-5 
18.3 
11.7 
16. 1 
12.0 
6.7 
15-2 
11.9 
Low prairie 
15.3 
22.3 
26.2 
21.5 
12.7 
16.3 
13.2 
8.5 
17.0 
Dogwood-bur 
oak shrub 
20.1 
26.9 
3I-I 
254 
19.4 
22.8 
19.6 
15. 1 
22.5 
Prickly ash-dog- 
wood shrub. . . . 
24.6 
29.1 
31-3 
27.7 
22.1 
24.0 
23-5 
15-3 
24.7 
Red oak-hickory 
forest 
28.5 
31.2 
36.0 
30.8 
25.3 
28.9 
25-1 
16.4 
27.8 
12.5 
Bur-oak forest . . . 
20.1 
24.8 
28.5 
23.1 
18.7 
21.8 
17.2 
11.7 
20.7 
12.5 
high prairie at o-io cm. four times and at 10-30 cm. two times during the 
growing season. In the bur-oak station it was unavailable once at both 
depths. Water was available for growth in the red oak-hickory station at 
all readings. The low water content in the high prairie was caused by the 
direct exposure to sunlight and wind, and by the great amount of run-off 
caused by the steepness of the slope. The bur-oak forest had a lower soil 
water content than the shrub stations because the plant cover was less 
dense. 
