RED PIGMENT OF FLOWERING PLANTS. 419 



trustworthy. They show that, in diffuse light and in a 

 fairly saturated atmosphere, transpiration even in the high 

 temperature of the tropics may be very low. Now 

 these are the conditions to which the shade-plants are 

 subject, and consequendy Stahl's theory, that the anthocyan 

 occurring in the leaves of such plants is of importance 

 in the service of transpiration, seems tenable. 



So much for the physiological side of Stahl's research. 

 It remains only to refer to experiments which he conducted 

 with a view to ascertain if any of the bright hues, character- 

 istic of tropical foliage, can be regarded as warning colours. 

 Since the bright colours of many flowers and fruits act as 

 decoys to insects and to birds, it seems a priori possible that 

 some of those of leaves may be of the nature of warnings 

 to ward ofl^ attack. 



Otto Kuntze (36) had, for instance, made the statement 

 that the Javanese plant hedges of a red-leaved plant to 

 warn away wild pigs. Stahl's inquiries, however, led him 

 to conclude that the Javanese choose the colour to please 

 themselves. 



The result of experiments on feeding various animals, 

 rabbits, sheep and goats on green and red leaves was that 

 the red does not, to any noteworthy extent, act as a warning 

 colour. In some cases the animals in question certainly 

 preferred the green leaves when quite similar in other re- 

 spects to the red ; but their prejudice gave way immediately 

 when the red leaves were more tender or in other ways more 

 desirable. 



To briefly summarise Stahl's work. There is no good 

 evidence for the screen-theory nor for that of warning leaf- 

 colours. Anthocyan is of importance by virtue of its heat- 

 absorbing properties. In temperate regions the heat so 

 absorbed facilitates translocation and general metabolism, 

 to the shade plants of the tropics it is an assistant to trans- 

 piration. 



A paper endeavouring to arrive at wide generalisations 

 by examining many of the scattered phenomena of colour to 

 be met with in plants and animals has recently been written 

 by Simroth {^'^"]). This author believes that all pigments 



