June, 1922] 
MUENSCHER ABSORPTION OF SALTS 
321 
gram of ash were reduced to approximately one half (table i). When trans- 
piration was reduced to one half by shading, the total dry matter and ash 
were reduced to considerably less than one half while the water requirement 
and the water used per gram of ash were increased considerably (table 2). 
These results seem to indicate that growth, as limited by food supply, 
rather than the rate of transpiration, determines the rate of absorption and 
total absorption of salts by plants. This view is strengthened by the fact 
that, in these experiments, the average percentage of ash expressed in terms 
of dry weight in whole barley plants of the same age is about the same 
regardless of whether transpiration was reduced by increasing atmospheric 
humidity or by decreasing the light intensity by shading. Table 3 presents 
a summary of the percentages, with probable errors, ^ of ash based upon the 
dry weights of tops, roots, and total plants, of the cultures grown under the 
various conditions in the summer series. Table 4 presents a summary of 
the percentages with probable errors of ash based upon green weights of the 
same cultures. 
There is no good criterion for measuring growth under all conditions. 
If total green weight is used., one must consider the variation in the 
water content in the tissues of the plants growing under various conditions. 
Data presented in tables i and 2 indicate that the water content of the 
plants grown in the humid atmosphere or in the shade is much higher than 
in plants grown in a dry atmosphere or in the open sunlight. This prob- 
ably explains the variation in ash content expressed as percentage of total 
green weight. Total dry weight seems to be a more satisfactory criterion 
for measuring growth in plants where large quantities of storage products 
are not formed. Table 3 shows a close relation between the weight of dry 
matter and ash content in barley plants regardless of the quantity of trans- 
piration. The variation in the average percentage of ash for the cultures 
grown under various conditions is only about five percent of the total 
ash. This shows a remarkable constancy in the percentage of ash in dry 
weight when compared with the great variation in the quantity of water 
absorbed per unit of ash content of the plants under the various conditions 
of this experiment. 
Table 3. Comparison of the Average Percentage of Ash Based upon the Dry Weight of 
Tops, Roots, and Total Plants {Averages of cultures in tables i and 2) 
Set of Cultures 
Percentage of 
Ash in Tops 
Percentage of 
Ash in Roots 
Percentage of 
Ash in Plants 
Dry chamber . . . 
Humid chamber 
Light 
Shade 
20.74 ± .027 
19.63 dc .026 
18.91 zt .017 
20.34 ± .027 
20.02 d= .020 
18.07 ± .030 
30.55 ± .043 
20.35 d= .048 
20.63 rb .024 
19.54 ± -013 
21.13 ± -OiS 
20.34 ± -024 
2 For the calculation of probable errors Bessel's formula was used. 
