284 BOTANICAL GAZETTE [APRIL 
function as limiting factors for photosynthesis, while light is usually 
present in excess. 
It is evident from the writer’s experiments that the reduction 
of light did not result in a lowering of the total production of plant 
substance; nevertheless, the production for equal areas of leaf sur- 
face was lower in the shade leaves than in the sun leaves. The 
reduction in photosynthesis in the shade leaves was compensated 
by an increase in leaf area, so that total production was not dimin- 
ished. 
Although shading, and the conditions brought about thereby, 
had no influence on the total elaboration of dry substance, the dis- 
tribution of dry substance was greatly affected. The distribution 
of the total dry matter among the various organs of the two sets 
of plants was as follows: 
TABLE XI 
Leaves Stems Roots 
aaa eee eae 
Sow plants. 2 525.4; 40 per cent 36 per cent 24 per cent 
Shade plants........ 36 per cent 42 per cent 22 per cent 
The proportion of material deposited in the roots was about the 
same in the two sets of plants, but the proportion deposited in the . 
leaves was much greater for the sun plants than for the shade 
plants, although the area of the shade leaves was nearly one-third 
greater than that of the sun leaves. This condition is in accordance 
with the general observation that rapidly transpiring leaves are 
thicker and of firmer structure than leaves developed under con- 
ditions of lower transpiration; or, as conversely expressed by 
SoRAUER,® of equal weights of fresh leaf substance that portion 
containing the greater percentage of dry matter transpires the more 
rapidly. The condition in the stems was the reverse of that in the 
leaves. In the shade plants the stems contained 42 per cent of the 
total dry matter of the plant, while in the sun plants only 36 per 
cent was deposited in the stems. It appears, therefore, that the 
shading exercises a distinct influence on the deposition of material 
in the stems and leaves, but that the influence affects the two organs 
39 SORAUER, P., op. cit, p. 391. 
