82 



Carbon Assimilation. 



which case increase of temperature produces no effect on the rate 

 of assimilation. The results have already been shown graphically 

 in Fig. 9. 



Blacknaan and Matthaei (1905) have also made extensive series 

 of observations on assimilation under different conditions of natui-al 

 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 throufjh 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 Heliantlnis tnherosns rmder 

 Natural Illwnination. 



Area of Leaf 70-1 sq. cms. 



800 c.c. of air containing 2-5% COj passed over the leaf per hour. 



Date: July 30th, 1904. 



Temperature 18-0° to 18-3°C. 



Assimilation at tills temperature when light is not limiting is 



•0093 gims. per 50 sq. cms. per hour. 



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. 



