Nov. 17,1923 
Absorption of Carbon by the Roots of Plants 
307 
direct sunlight, which made it necessary to spray one side of the bell jar 
with whitewash to prevent the plants from being blistered. The plants 
grown under the bell jar had as good a color as those grown outside, and 
were quite thrifty, but showed a greater tendency to spindle up on 
account of the modified light. The dry weights were taken as an indi¬ 
cation of the amount of cellulose and other organic compounds which 
had been formed under the various conditions. Since this seemed fairly 
accurate, no direct determination of the carbon was made. 
It will be seen by reference to the tables that the plants grown in the 
open increased about 100 per cent in dry weight over those having the 
same treatment but grown under bell jars. The plants in numbers 4 
and 7, Table III, had an abundance of carbon in solution as a carbonate, 
but did not seem able to utilize it in tissue building. The variation in dry 
weight was rather wide, as might have been expected, but by comparing 
the plants in each culture pan grown under a bell jar with those in a 
pan having the same treatment but grown in the open, it seems quite 
evident that the plant is unable to substitute, to any appreciable ex¬ 
tent, the carbon of the C0 3 radical absorbed by the roots for the carbon 
of the carbon dioxid taken in by the leaves. 
In the experiments here recorded there are suggestions that the carbon 
needed for building up organic compounds in the plant is derived from 
the carbon dioxid of the air, and not from the C 0 3 taken into the plant 
through the roots. Nevertheless, it is evident that plants demand C 0 3 , 
and will absorb it under certain conditions, to the benefit of the plant. 
The writer finds it advantageous to have a little calcium carbonate 
present in nutrient solutions, or, if this is not feasible, a little sodium 
carbonate. 
The stimulative influence of sodium carbonate is noticeable in soils 
that have a small amount of black alkali. In many instances the bene¬ 
ficial effect of sodium nitrate seems to be partly due not only to the 
nitrate radical (NO s ), as is generally supposed, but also to the excess 
of the base which the absorption of N 0 3 leaves in the solution to act as 
a go-between in indirect absorption of carbon dioxid by the plant. 
The experiment has been performed of taking two portions of the 
same nutrient solution, each containing 100 ppm. of sodium nitrate, 
keeping in one a large number of healthy wheat seedlings for a few 
days until the nitrate radical, N 0 3 , is entirely absorbed, then removing 
the seedlings, placing small seedlings in both portions and allowing them 
to grow. When this growth begins, one portion of the nutrient solution 
still contains 100 ppm. of sodium nitrate, or about 72 ppm. N 0 3 avail¬ 
able as plant food, while the other has no nitrates. For two or three 
weeks the plants are often found to grow equally well in the two 
solutions. Both solutions contain approximately the same amount of 
sodium, as a nitrate in one case and a bicarbonate in the other. A wheat 
plant of course can not continue to grow indefinitely without an ade¬ 
quate supply of nitrogen; but during the seedling stage, while there is 
still some plant food stored up in the seed, the plants will often grow 
equally well in the two nutrient solutions. 
The writer has observed that the ash of the so-called “lime-loving’’ 
plants usually runs very high in carbonates, while the ash of plants 
that have been grown upon acid upland soils often runs extremely low 
in this respect. This may be true of acid-loving plants like the blue¬ 
berry and cranberry, which grow best in acid lowland soil, but adequate 
