Ewart . — The Effects of Tropical Insolation . 479 
influence of light on translocation, but may be indirectly due 
to the light causing a markedly increased transpiration, and 
so increasing the velocity of the conduction-currents as to 
rapidly remove the soluble carbohydrate as fast as it is 
formed, thereby permitting of the rapid solution and removal 
of the accumulated starch. At the same time it is in the 
early morning, as the temperature rises, and before the light 
becomes too strong, that growth is most active, and the stored 
material is most rapidly used up. 
There can be little doubt that, both in the tropics and in 
temperate climes, the main and primary function of the red 
dye, when present in exposed parts, is to act as a protection 
against light of too great intensity; though in all cases its 
presence at the same time confers upon the plant a slightly 
increased power of absorbing heat. For calling attention to 
this latter possibility Stahl deserves full credit from both the 
physiologist and the biologist : in a few cases, such as in the 
horizontal leaves of shade plants having the red colouration 
present on the under surfaces only, the relatively slight heat- 
absorbing power of the red dye may, by secondary adaptation, 
have become its most important function. 
Summary. 
In tropical plants full and prolonged insolation may 
markedly affect or temporarily inhibit the functional activity 
of the assimilating parts. If the stoppage be temporary, it 
is generally accompanied by but little change in colour ; but 
if permanent, the colour of the chlorophyll-grains is markedly 
affected, and they may be completely bleached. Different 
plants show very different resistant powers, shade-loving plants 
being, as might naturally be expected, the least resistant. 
The leaves are protected against the injurious effects of 
excessive exposure by the presence of a red dye and by 
active or passive paraheliotropic movements. The active 
movements are best shown by the motile leaves of the 
Leguminosae, the pulvini being the motile and irritable 
