470 Ewart . — The Effects of Tropical Insolation. 
trees, Keeble 1 has already shown that the hanging position 
acts as a protection against excessive transpiration which 
is very apt to injure the young leaves, and that when in 
addition a red dye is present the decomposition of the chloro- 
phyll by exposure to strong light is thereby largely prevented. 
The temperature-determinations which Keeble made at the 
upper and under surfaces of red and green insolated leaves 
of Anther stia nohilis , seem to point to the following explana- 
tion. On the upper surface of the red leaf the temperature 
averages i°C higher than on the upper surface of the older 
green leaf, owing to the transpiration being less and the 
absorption of heat being greater in the former case than in 
the latter ; whilst at the under surface of the green leaf the 
thermometer averages a degree above that beneath the red 
leaf, owing to the green leaf being more transparent to radiant 
heat than the red one is. Any injurious increase in the rate 
of transpiration, which might be caused in the young red 
leaves by the slight increase in the power of heat-absorption 
which the red colouration gives them, is prevented by their 
overlapping and hanging position. 
It is evidently of considerable interest to know exactly 
what power of assimilation the young leaf possesses when 
in the hanging position. The following observations made in 
the usual manner elucidate this point, the measurements 
in length (L) and breadth (B) being given in terms of those 
of the fully adult leaf: — 
Saraca declinata , L T 8 T , B T 6 T . Very pale yellowish green, apical half 
pinkish white. No power of assimilation perceptible except along 
the veins, here the chlorophyll grains are small pale yellowish green 
and faint evolution of O is shown. L f, B T 7 T . Pale yellowish green, 
distinctly green along the veins, apical portion pinkish white. 
Chlorophyll-grains moderately large, weak assimilation, moderately 
active at base near ribs, in apical portion faint or imperceptible. 
L f , B t 8 t . Chlorophyll-grains fairly large and green, assimilation 
active to moderately active, leaflets green and expanding. 
1 Annals of Botany. 
