460 Ewart. — The Effects of Tropicat Insolation . 
Protective Red Dye. 
In a very large number of cases, and more markedly in the 
tropics, the leaf, especially when young, is partly shielded 
from the effects of exposure to light by the presence of a pro- 
tective red dye. Stahl, in a recent publication 1 , has expressed 
certain theories with regard to the function of erythrophyll 
in plants, which cannot be passed over without criticism. 
In opposition to the generally accepted view, Stahl holds 
that the importance of the red dye is that it acts, not as 
a protection against light at all, but first, as a warning or 
frightening ( abschreckende ) colouration, and secondly, and most 
importantly, as a heat-absorbing medium. 
As regards the importance of the red dye as a frightening 
colouration, Stahl himself shows that it only applies to higher 
animals in which the powers of vision, and more especially 
of colour-perception, are well developed ; and even then the 
deterrent effect is by no means marked, and ceases to become 
evident when the animal is hungry. Obviously, with animals 
such as snails, the main depredations of which are carried on 
in darkness or in partial obscurity, when the red colouration 
cannot be distinguished, it can hardly exercise any deterrent 
effect in virtue of its colour. It may safely be concluded 
that any value of the red dye as an ‘ abschreckende ’ coloura- 
tion is quite accidental and secondary, though it may 
in some cases be of undoubted use to the plant. A similar 
instance, in which a special peculiarity developed for a par- 
ticular purpose has acquired accidentally a minor secondary 
importance, is afforded by Mimosa pudica . In this plant the 
folding up of the sensitive leaflets, which takes place when 
the plant is agitated by the wind, is undoubtedly of primary im- 
portance as a protection against mechanical injury or drought, 
to both of which the plant is very sensitive and liable. When 
a browsing animal, such as a goat, approaches a clump of 
1 Stahl, Ueber bunte Laubblatter : Ann. d. Jard. Bot. de Buitenzorg, Vol. 
xiii, 2 e partie, p. 137, 1896. 
