466 Ewart . — The Effects of Tropical Insolation . 
leaves (5 cm. long by 2*2 cm. broad) show normally a weak 
but distinct power of assimilation, but after eight hours 
exposure to full sunlight, with the dorsal surface upwards, 
assimilation is faint or absent, some leaves being fatally 
injured ; whilst if the ventral surface, exposure of which in an 
adult leaf of a shade-plant sensitive to exposure produces 
more effect than does exposure of the dorsal surface, is 
subjected to insolation for the same time, a weak or faint 
power of assimilation is shown, and the leaves all recover and 
show next day a normal weak power of assimilation. In 
a fully adult green leaf (13*5 cm. long by 6-5 broad) after 
eight hours’ exposure, a moderately to fairly active power 
of assimilation was shown. 
An unnamed epiphytic Aroid, growing in the Canarien 
Allee near the main entrance of the Buitenzorg Gardens, has 
the young leaves rolled up vertically with the ventral (under) 
surface outwards, a red dye being present in the spongy 
mesophyll-cells and also around the vascular bundles. As 
the leaf expands horizontally, dorsal surface upwards, the red 
dye lessens in amount ; but in adult leaves a slight amount is 
still present. In other plants the red dye might remain in 
this position in the adult leaf as a vestigial survival of that 
present in the young leaf, and without necessarily having any 
functional importance. 
In many Scitamineae it is the under surface of the leaf 
which is red. Alpinia officinarnm , Hance, has a purplish-red 
colour, on the under surfaces only, of the nearly vertically 
erect leaves. From the very young leaves the red colour 
is absent ; it appears as soon as the leaf is exposed, and is 
most marked when from one-third to one-half full grown ; after 
this it decreases in amount, disappearing at the edges and 
sides first, and finally in the fully adult leaf being totally 
absent. Belemcanda chine nsis is exactly similar with regard 
to the distribution and appearance of the red dye, but the dye 
does not commence to disappear until after the leaf is fully 
adult and the young sensitive growing tissues no longer need 
that protection from light which, owing to the marked 
