Dioxide Absorption of Coco-nut Leaves . 375 
which the abscissae represent the hours at which each test period ended, 
and the ordinates represent rates of carbon dioxide absorption in grammes 
per square metre per two hours. 
It will be seen that the amounts of carbon dioxide absorption from 
5.30 to 7.30 a.m. and again from 5.30 to 6.30 p.m. were negligible, since 
they represented in both cases the minimum amounts of acid which were 
measured in the titrations, i. e. 0*05 c.c. Thus the really effective period of 
carbon dioxide absorption was during ten hours, from 7.30 a.m. to 5.30 p.m., 
and the maximum rates of absorption occurred at 7.30 to 9.30 a.m. and 
3.30 to 5.30 p.m., there being thus a midday depression which reached its 
lowest point at 11.30 a.m. to 1.30 p.m. This depression was during an 
interval of bright sunshine, as shown by the observations in Table I, and was 
also at the time when the sun is most directly overhead, so it may have been 
caused by excessive insolation. Or it is quite as possible that something 
connected with the internal metabolism of the leaf, and not any particular 
set of atmospheric conditions, may be responsible for this rather peculiar 
behaviour. 
For an approximate comparison of carbon dioxide absorption and the 
gain in dry weight of the leaf, the two leaves used in this experiment were 
plucked in the morning. One half of each was measured, weighed, and 
dried in the morning, and the remaining halves were exposed ; one inside 
the apparatus (test leaf), and one outside (exposed leaf) beside it, as was 
stated above. These latter were measured and dried at 6.30 p.m. The 
results are given below. 
Table III. 
Comparison of increase in dry weight of detached half-leaves, one inside 
the glass tube of the apparatus and the other fully exposed to the sun 
during one day. 
Leaf designation. 
\ of tested leaf. 
t> „ | leaf 
\ of exposed leaf 
„ „ | leaf 
Dried at 
Areas in 
Dry wt. 
Dry wt. per 
sq. m. in 
Apparent 
gain in dry 
sq. cm. 
in grm , 
grm. 
wt. per sq.m, 
grm. 
6.30 p.m. 
194.87 
1.416 
72-66 
5.30 a.m. 
171.63 
1*172 
68.22 . 
4*44 
6.30 p.m. 
160.53 
1.204 
75-o 
5.30 a.m. 
186.77 
i* 3 i 6 
70.46 
4'54 
The apparent gain in dry weight of the leaf inside the apparatus was 
thus 4-44 grm. per sq. m. But Kuijper has shown 1 that usually the outer 
side of the sugar-cane leaf, which is the side covering the rolled leaf in the 
bud, is smaller in area, has more veins per unit area, and is usually heavier 
in dry weight per sq. m. than the inner side by about i-6 grm., in at least 
one variety of cane. It has also been shown by Thoday 2 that most 
leaves shrink during the day, sometimes as much as 1 per cent, of their 
1 Kuijper, J., cited above on p. 371. 
2 Thoday, D., cited above on p. 367. 
