3°6 
Journal of Agricultural Research 
Vol. XXVI, No. T 
of some difference in ionization now not recognized, or, more probably, 
may be due to the exceedingly small amount of C 0 3 and HCO s ionized. 
Carbon is one of the most important elements entering into a plant s 
composition. We have been taught that the source of supply of carbon 
is the carbon dioxid of the air, and that the absorption of this gas takes 
place through the leaves of the plant. Evidently, judging from the ex¬ 
periments just described, there is another source of carbon, and another 
way of absorbing it into the plant system. 
We are also accustomed to think that the only use of carbon in the 
plant's economy is in building up organic compounds, such as cellulose. 
Considered as the atom carbon, this may be true, but it seems reason¬ 
able to assume that a plant would not demand the radical C0 3 unless 
it had some special use for it. To determine if carbon derived from 
this source can be used by the plant in building up cellulose and similar 
compounds, the following experiments were conducted: 
Culture pans, each containing 175 wheat seedlings, were grown out- 
of-doors, in cool weather, for 60 days, using distilled water, with and 
without salts in solution, and under other conditions described in Tables 
III and IV, and the dry weights of 100 plants from each pan determined. 
Table III.— Dry weights of wheat plants grown under specified conditions {first series) 
No. 
Conditions. 
Dry weight, 
100 plants. 
I 
Distilled water, pan uncovered. 
Gm. 
5-850 
2. 617 
6.634 
3.667 
6.456 
2.764 
2. 9OO 
2 
Distilled water, covered with a bell jar and sealed with adhesive 
tape against outside air. 
3 
Distilled water, with excess of CaC 0 3 , uncovered. 
4 
Distilled water, with excess of Ca 0 O 3 , covered with bell jar with a 
water seal. 
5 
Distilled water, with 137 ppm. NaN 0 3 , uncovered. 
6 
Ditilled water, with 137 ppm. NaN 0 3 , covered with bell jar and 
sealed with tape. 
7 
Distilled water, with 137 ppm. NaN 0 3 and excess Ca 0 O 3 , covered 
with bell jar and water sealed. 
Table IV.— Dry weights of wheat plants grown under specified conditions {second series) 
No. 
Conditions. 
Dry weight, 
100 plants. 
I 
Distilled water, uncovered. 
Gm. 
4. 76 
3-23 
6. 11 
2 
Distilled water, covered with bell jar and hermetically sealed 
with paraffin. 
3 
Distilled water, with 137 ppm. NaN 0 3 and excess of CaC 0 3 , un¬ 
covered. 
4 
Distilled water, with 137 ppm. NaN 0 3 and excess of CaC 0 3 , cov¬ 
ered with bell jar and hermetically sealed. 
3-85 
Since the amount of carbon dioxid originally contained in the air of 
the bell jar in each case was insignificant, no attempt was made to wash 
it out before beginning the experiment. The plants were grown in the 
