322 
AMERICAN JOURNAL OF BOTANY 
[Vol. 9, 
Table 4. Comparison of the Average Percentage of Ash Based upon the Green Weight of 
Tops, Roots, and Total Plants {Averages of cultures in tables i and 2) 
PercentaRe of 
Percentage of 
Percentage of 
Set of Cultures 
Ash in Tops 
Ash in Roots 
Ash in Plants 
Dry chamber 
1.92 zb .030 
1. 00 zb .024 
1.69 =b .026 
Humid chamber 
1. 61 ± .022 
.93 =h .024 
1.46 ± .016 
Light 
1.88 ± .028 
2.01 ± .046 
1. 91 ± .019 
Shade 
1.93 ± .031 
•95 ± -036 
1.68 =b .026 
Winter Series 
Light-Shade Cultures 
A series of cultures was set up during the winter in order to check the 
results obtained by shading plants in the summer experiment. Table 5 
presents a summary of the data obtained. The data are self-explanatory 
and check very closely with the light-shade cultures of the summer series. 
The absolute values for green weight, dry weight, and ash weight are sHghtly 
lower throughout, but relatively the results duplicate those of the summer 
series. The water requirement and the quantity of water used per gram 
of ash content were increased considerably in the plants growing in the shade 
under conditions of low transpiration. This relation holds not only between 
the shaded and unshaded plants within the summer and winter series, but 
also between the summer and winter series. The plants growing on an 
exposed greenhouse bench and in a shade tent in winter receive much less 
sunlight than plants growing under similar conditions in the summer. 
Table 5. Relation of Ash Content in Barley Plants to the Amount of Transpiration as 
Affected by a Difference in Light Intensity. Winter Series. Plants 
Grown 5 Weeks (January ig to February 24, 1921) 
Light 
Shade 
Tops 
Roots 
Plants 
Tops 
Roots 
Plants 
No. of cultures averaged 
12 
II 
Green weight per culture (grams) 
6.97 
3.01 
9.98 
4-34 
6.09 
Dry weight per culture (grams) . 
.765 
.150 
.915 
.408 
.052 
.460 
Total ash content per culture 
(grams) 
•151 
.031 
.182 
.078 
.009 
.087 
Ash content (percentage of green 
weight) 
2.16 
1.02 
1.82 
1.80 
0.51 
1.43 
Ash content (percentage of dry 
weight) 
19.70 
20.51 
19.83 
19.56 
17.21 
19.30 
Total water transpired (cc.) .... 
659.6 
382.7 
Water used per gram dry matter 
(cc.) 
720.87 
831.95 
Water used per gram ash con- 
tent (cc.) 
3,624.17 
4,398.85 
This probably explains the increase in water requirement and in quan- 
tity of water used per gram of ash content in the plants of the winter series. 
