75 
certain Tropical Trees . 
exposure to the sun, serve as the red sap of Amherstia nobilis 
seems to serve — not only as light-screens, but also as heat- 
screens, whereby the fierceness of the sun’s rays is tempered to 
the young leaf ; and although a difference of a degree — that 
recorded in the case of Amherstia nobilis — is not actually 
much, in times of danger it might mean the difference between 
life and death, or at all events between impaired or unim- 
paired functional activity and development. 
In the group of trees under consideration this means of 
protection is not universal ; and indeed it is only suggested 
that it seems to be a minor adaptation, which makes for the 
security of the young foliage whilst in its limp thin condition. 
That it does not occur in all by no means destroys this con- 
tention, since, to some trees, the production of coloured sap is 
a more simple task than to others. Thus it would seem to 
be simple to Amherstia nobilis , since the red colour not only 
characterizes the young foliage, but appears in the flower, the 
fruit, the buds and the flower-stalk. 
In such trees as Humboldtia lanrifolia , whose hanging 
foliage is white, it may be that greater thickness of cuticle is 
earlier arrived at, or that a slightly different habit or habitat 
renders such a minor adaptation of less importance. 
Another factor, which in Amherstia nobilis may serve to 
reduce the temperature of the leaves, is their fugitive hairy 
covering. It is a curious point that these hairs, which render 
the young leaves of Amherstia nobilis very difficult to wet, 
disappear in the mature leaves ; although, according to Stahl, 
it is those very mature leaves which need protection against 
wetting. That these mature leaves need some means whereby 
rainwater may be rapidly carried away from the leaf Stahl infers 
from their possession of a very long acuminate apices, to which 
in such and similar cases he has given the name of ‘Traufel- 
spitzen 5 (drip-tips). Stahl finds from experiment and obser- 
vation on many species of plants that these acuminate apices 
are very useful in carrying away water which falls on the leaf 1 . 
t 
1 Cf. also Junger’s view, Bot. Centralblatt, 47, No. 12, who suggests a similar 
function for these acuminate apices. 
