Carbon Assimilation. 
»57 
which case increase of temperature produces no effect on the rate 
of assimilation. The results have already been shown graphically 
in Fig. 9. 
Blackman and Matthaei (1905) have also made extensive series 
of observations on assimilation under different conditions of natural 
illumination which show strikingly the influence of light as a limiting 
factor. The general arrangement of the experiments was similar 
to that employed previously and referred to in the previous section 
of this chapter. The leaves experimented upon were contained in 
a leaf chamber as before through which a current of carbon dioxide 
was passed such that the supply of carbon dioxide never limited the 
intake of the gas. The experiment summarised in the following 
table may be regarded as typical. 
Table XIII. 
Assimilation by a leaf of Helianthus tuberosus under 
Natural Illumination. 
Area of Leaf 70-1 sq. cms. 
800 c.c. of air containing 2*5% C0. 2 passed over the leaf per hour. 
Date : July 30th, 1904. 
Temperature 18-0° to 18-3°C. 
Assimilation at this temperature when light is not limiting is 
•0093 grms. per 50 sq. cms. per hour. 
Time 
P.M. 
Illumination. 
Temp. 
of 
Bath. 
C0 2 in grams 
absorbed by 
leaf. 
Real assimila¬ 
tion in grams 
C0 2 per 50 sq. 
cms. per hour. 
12.30-1.30 
— 
— 
Preliminary 
Preliminary 
1.30-2.30 
Heavy laden clouds 
Violent thunderstorm 
18-2 
0 0011 
0 0015 
2.30-3.30 
at first; then slowly 
18-3 
0-0032 
00030 
clearing up 
3.30-4.30 
Brighter; no rain 
183 
0 0073 
0 0059 
4.30-5.30 
Sun at first, then clouded 
over ; storm driving up 
18-3 
0 0050 
0-0043 
5.30-6.30 
Overcast, steady rain ; 
6* 10, heavy storm 
180 
0-0007 
0 0010 
It will be observed that the intake of carbon dioxide is in none 
of these measurements near the value given when light is not 
limiting, and in each case the assimilation must be a measure of 
the light only. The assimilation shows marked variations parallel 
with the light conditions. 
