Ewart . — The Effects of Tropical Insolation. 473 
having more or less reddish young leaves. Yet it is just here 
where a power of stimulating transpiration is apparently most 
needed ; for at this elevation the air is, during the greater 
part of the time, at or near saturation -point. On the other 
hand if the red pigment acts as a protection against sunlight, 
it is easy to understand why here, where the sun rarely shines 
for more than a few hours daily and then generally through 
a haze of clouds, the protective red pigment should almost 
entirely disappear; for it is just the more refrangible photo- 
chemical rays which the air saturated with water-vapour 
absorbs in greatest amount. 
At the summit of Pangerango (10,000 ft.) and for a few 
hundred feet below, the plants are in one or more character- 
istics markedly xerophilous (hairs, wax, thick epidermis and 
cuticle, few stomata, mucilaginous or fleshy tissues, reduced 
leaf-surface, &c.), and very many have a pronounced red 
colouration either in the young leaves and shoots or in the 
adult leaves as well. Here, just above the cloud-belt, the 
exposure to light is greater both in amount and intensity; 
whilst the drier air, the lower atmospheric pressure, and the 
more prevalent wind, all render the rapid evaporation of 
water easy. From too intense exposure to light the plants 
protect themselves largely by means of the red pigment ; 
whilst the xerophilous character which the plants assume 
guards them against excessive transpiration, to which the 
difficulty of absorbing water in sufficient amount when the 
ground-temperature is low but the temperature around 
the aerial parts relatively high, a frequent occurrence at 
such elevations, renders them especially liable. It appears 
therefore that where transpiration is easy but the exposure 
to light great, the red colouration is most marked, but where 
transpiration is difficult and the exposure slight, it diminishes 
or disappears. 
In Java at the commencement of the wet S.W. monsoon 
and in Ceylon at the rainy commencement of both monsoons, 
the vegetation acquires a more marked reddish tinge than 
in the dry periods between the monsoons. This is, however, 
