Carbon Assimilation. 
Table XLI. 
The Absorption of Radiant Energy by the Leaf in the Presence 
and in the Absence of Carbon Dioxide (Puriewitsch ). 
Species. 
Date. 
Duration of 
Experiment. 
co 3 
in 
air, per 
cent. 
Ratio of Energy 
trasmitted in 
presence of 
CO 2 to that 
transmitted in 
absence ofCO, 
per cent. 
Ratio of Excess 
of Energy ab¬ 
sorbed by the 
leaf in presence 
of C 0 1 to that 
transmitted in 
absence of CO, 
percent. 
Aristolochia Sipho 
27 May 1910 
11.25 a.m.-12.43 p.m. 
1-2 
95-0 
5-0 
1.1—2.8 p.m. 
J J 
90-4* 
9-6 
»i n 
) > > J 
11.25 a.m.-12.43 p.m. 
> » 
92-2 
7-8 
1.1-2.8 p.m. 
1 i 
95-4* 
4-6 
Catalpa speciosa 
1 June 1910 
11.55 a.m.-TO p.m. 
0-7 
99-0 
1-0 
Acer platanoides 
2 June 1910 
11.29 a.m.-1.14 p.m. 
1-7 
98-3 
1-7 
♦The values marked with an asterisk were obtained by means of a Rubens 
thermopile, the remainder by means of the Bolometer. 
Brown and Escombe suppose that the total radiant energy 
falling on the leaf is used in the following ways ; 
(1) in assimilation, 
(2) in transpiration, 
(3) by transmission through the leaf, 
(4) by thermal emission (if the leaf temperature is higher than 
that of its surroundings, as it usually is, this is positive, but if lower 
the thermal emission is negative, that is, the leaf gains energy from 
its surroundings). 
We have indicated earlier in this chapter that Brown and 
Escombe estimated the assimilation by calculating the increase in 
dry weight from the intake of carbon dioxide and the assumed heat 
of combustion of the products. Thus, in this first determination, 
two assumptions are made, the accuracy of which are not 
confirmed by measurement. One of these is the assumption that 
1 gram of carbon dioxide absorbed is equivalent to 0-64 gram of dry 
matter ; the other that the heat of combustion of the products is 
3-76 x 10 3 gram-calories. 
The transpiration was determined by weight, and the energy 
used in transpiration calculated from the heat of vaporisation of 
water at the particular temperature. 
The energy transmitted was calculated from the coefficient of 
absorption of the leaf, which was found in the following manner. 
A day of bright sunshine was selected and the intensity of radiation 
