Dioxide Absorption of Coco-nut Leaves. 383 
In Table V the total amounts of carbon dioxide absorbed per square 
metre of leaf surface are shown to be all very low ; the amount for the most 
rapid leaf, i.e. for leaf 2, is only about one-sixth of the corresponding value 
for the detached sugar-cane leaf. This indicates that either the rate of 
photosynthesis in coco-nut is very slow or the carbon supply is supple- 
mented from some other source than from carbon dioxide absorbed from 
the air by the leaf. It is possible that the coco-nut, with its massive trunk, 
may store organic acids and reconvert them to carbohydrates during 
sunlight. 
A comparison of the different leaves (though treated on different, but 
very similar days, as shown by the weather records and observations) 
indicates that the rate of photosynthesis is most rapid in the middle-aged 
leaves. Leaves 2, 3, and 4 agree in having a much more rapid rate of 
carbon dioxide absorption than leaves 1 and 6. Leaf 1 was markedly 
immature, the pinnae not yet being spread apart at the time of testing. 
Since the lower surface, bearing the majority of the stomata, was not yet 
even exposed to the air, the leaf was quite naturally sluggish. Leaf No. 6, 
although apparently healthy, had assumed a slightly yellowish-green tint, 
quite distinct from the brilliant dark green of leaves 2, 3, and 4. Thus 
coco-nut agrees in this respect with most other plants studied hitherto, in 
that the maximum rate of carbon dioxide absorption is performed by the 
young, but fully developed leaves. 
The diurnal march of carbon dioxide absorption is best seen in the graphs, 
Diagrams 2 to 6, which are constructed like Diagram 1. All of these 
graphs, though differing in details, show an early maximum rate, followed by 
a depression in rate of carbon dioxide absorption in the middle part of the 
day, again followed by a secondary rise in the rate just prior to the decline 
towards sunset. In leaves 1, 2, and 4 this daily march is quite uniform, the 
first maximum occurring in the period from 5.30 to 7.30 a.m. and the second 
maximum at 1.30 to 3.30 p.m. In the test of leaf 3 this is less apparent, 
there being the first maximum between 7.30 and 9.30 a.m. and a much less 
pronounced second maximum at 11.30 to 1.30 p.m. Leaf 6 has a well- 
marked maximum between 10 30 a.m. and 12 30 p.m. The above data, all 
except leaf 6, show an initial maximum rate of carbon dioxide absorption 
by coco-nut, followed later in the day by a secondary maximum. This 
behaviour closely parallels the behaviour of many plants in transpiration, as 
shown by Shreve, 1 and might suggest that this phenomenon likewise may 
be due to incipient drying. To test this approximately the measurements of 
the spread of the coco-nut pinnae are introduced in Diagrams 3 to 6. The 
graphs of spread of pinnae show minima, i.e. minima of water content of 
leaves, at hours varying from 12.30 to 4.30 p.m., and these minima show no 
1 Shreve, E. B. : The Daily March of Transpiration in a Desert Perennial. Carnegie Inst., 
Wash., Publ. No. 194 (1914). 
