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AMERICAN JOURNAL OF BOTANY 
[Vol. 9, 
the plants. This Hmited the amount of food available for growth, and as a 
result of checked growth smaller quantities of inorganic nutrients were used. 
The total ash expressed as percentage of dry weight was only about four 
percent less (ratio, light to shade = lOO : 96.3) in the shaded plants. 
Expressed as percentage of green weight the ash was about twelve 
percent less (ratio, light to shade = 100 : 87.9) in the shaded than in the un- 
shaded plants. 
The total transpiration per culture for the period of five weeks was 833 
cubic centimeters in the unshaded as compared with 400 cubic centimeters 
in the shaded cultures. The water requirement, contrary to the common 
idea that this always increases under conditions favoring high transpira- 
tion, decreased from 672 in the shaded cultures to 546 in the unshaded cul- 
tures which actually transpired more than twice as much as the shaded 
plants. The amount of water transpired per gram of ash was considerably 
less in the unshaded plants than in the shaded ones. This is just the oppo- 
site of the results obtained when transpiration was doubled by decreasing 
the atmospheric humidity, which doubled both the water requirement and 
the water used per gram of ash (table i). 
These data agree with those of Schloessing (1869) who found that a 
tobacco plant grown under a shaded bell jar had a smaller total ash content 
and a smaller dry weight than plants grown in the open. When the plant 
was shaded, not only was transpiration reduced, but the amount of avail- 
able food was also limited, growth was checked, and the plant utiUzed 
smaller quantities of inorganic nutrients. Hasselbring (1914 a) did not 
find a reduction in total ash content or dry matter by shading tobacco 
plants. It is probable that light was not reduced enough to become a limit- 
ing factor for tobacco plants under the conditions of his experiment in Cuba. 
His shaded plants were much larger than those grown in the open, and per- 
haps the increased photosynthetic area was enough to offset any reduction 
in the rate of photosynthesis due to shading. In the experiment reported 
here light was a limiting factor. 
The data presented in table 2 show that, when transpiration was re- 
duced by shading, the total ash content was also reduced. This might lead 
one to infer that there exists a relation between transpiration and the ab- 
sorption of salts. It must be remembered, however, that, when transpira- 
tion was reduced by shading, the photosynthetic activity was also reduced 
at the same time, as is shown by the fact that both green and dry weights 
of the shaded plants were less than one half as great as those of the plants 
that were not shaded. If checking the transpiration alone were responsible 
for the reduced ash absorption, then the results of the dry-humid cultures 
presented in table i should correspond with the results of the light-shade 
cultures in table 2. These data show that when transpiration is reduced 
to one half by increasing the humidity, the total dry matter and ash were 
reduced only slightly and the water requirement and the water used per 
