Field Studies of the Carbon Dioxide Absorption 
of Coco-nut Leaves. 
BY 
F. T. McLEAN. 
With Plate XVIII and nine Diagrams in the Text. 
T HE fixation of atmospheric carbon dioxide is undoubtedly the most 
important function of green plants. The rapidity of this process as it 
goes on in growing crops is an index of the food-manufacturing power of the 
plants. The effects of different environments and of different methods of 
culture on the carbon dioxide absorption may therefore serve as an imme- 
diate index of the value of such environment or treatment. This problem 
has been attacked in the past with a few crops by either analysing leaves 
gathered at intervals during the day 1 or by determining the increase in dry 
weight of leaves . 2 
Obviously neither of these methods can give a measure of the total 
photosynthesis of leaves attached to growing plants. Either the leaves 
must be detached, and then the accumulation of the products of photo- 
synthesis interferes with the process unduly, as shown by Ewart ; 3 or if the 
leaves remain on the plant, the translocation of materials away from them 
diminishes the accumulation and thus diminishes the apparent amount of 
photosynthesis as measured by either analysis or by dry weight increase. 
Apparently the most satisfactory method for measuring the process is 
by the determination of the gas exchange, or of one phase of it. Since the 
amount of carbon dioxide fixed by the plant is of more importance to plant 
nutrition than is the amount of oxygen evolved, it seems preferable to 
measure the carbon dioxide absorption. This can only be successfully 
accomplished by enclosing the leaf in some sort of chamber, thus altering 
conditions surrounding it and modifying the rate of carbon intake. 
1 A review of results obtained by this method is given in : 
Atkins, W. R. G. : Some Recent Researches in Plant Physiology. Whittaker and Co., London, 
1916. 
2 Thoday, D. : Experimental Researches on Vegetable Assimilation and Respiration. V. A 
Critical Examination of Sachs’ Method for using Increase in Dry Weight as a Measure of Carbon 
Dioxide Assimilation in Leaves. Proc. Roy. Soc., London, B., lxxxii. 1-55, 1909. 
3 Ewart, A. J. : Assimilatory Inhibition in Plants. Jour. Linn. Soc. Bot., xxxi. 364-461, 1896. 
[Annals of Botany, Vol. XXXIV. No. CXXXV. July, 1920.I 
