389 
Dioxide Absorption of Coco-nut Leaves. 
The above results show that the rates of absorption of abaca leaves are 
not widely different in full sunlight from those of coco-nut pinnae, and are 
much lower than that of sugar-cane. Further, each of the two abaca tests 
shows a maximum rate of carbon dioxide absorption very early in the 
morning, and the first, as shown in Diagram 8, has a second maximum at 1.30 
to 3.30 p.m., which is not exhibited by the second abaca test (Diagram 9). 
Comparisons between these two tests would not be relevant, since the two 
leaves may not have been of comparable age, and no study was made of the 
effect of age on the photosynthetic activity of abaca leaves. 
Conclusions. 
1. The method here described for field studies of carbon dioxide 
absorption by leaves is satisfactory for comparative studies of the rates of 
carbon dioxide absorption by different leaves, by the same leaves at 
different times, and by the leaves of different kinds of plants. 
2. Middle-aged leaves absorbed carbon dioxide faster than either 
immature or old leaves. Of the five leaves of the coco-nut which were 
tested on one plant, the youngest leaf, which was not yet unfolded, „and the 
oldest healthy-looking leaf (No. 6) both showed very low rates of absorption. 
The three young, fully expanded leaves all showed comparatively rapid 
rates. 
3. The rates of absorption of carbon dioxide by coco-nut leaves show 
a maximum rate in the morning, a depression at midday, and a second rise 
in the afternoon, followed by a final decline towards sunset. 
4. Detached pinnae of coco-nut absorb carbon dioxide at about the 
same rate as similar leaves attached to the plant, but the maximum occurs 
at a different time of day from that of attached coco-nut leaves. 
5. Comparisons of carbon dioxide absorption by coco-nut leaves with 
that by the sugar-cane and abaca leaves tested indicate that sugar-cane 
absorbs much more rapidly than coco-nut under the conditions encountered 
during these tests. 
University of Philippines, 
College of Agriculture, 
Los Banos. 
March 20, 1918. 
