62 
COLOUR IN NATURE 
CHAP. 
found by experiment that the red parts of plants 
absorbed 1.82 per cent more heat than green parts, 
and he considers that this fact explains the peculiar 
distribution of this red colouring-matter, its presence 
in young shoots, Alpine plants, etc. He believes 
that it also explains its occurrence in wind-fertilised 
flowers, in many Dicotyledons, in Gymnosperms, in 
Cryptogams, and so on, for the increased absorption 
of heat in these cases would aid the growth of the 
pollen tube, etc. It does not, however, explain the 
occurrence of red pigment in the leaves of tropical 
plants, where it is often associated with the simul¬ 
taneous occurrence of white spots, which have, of 
course, exactly the contrary effect as regards heat 
absorption. Stahl finds that such plants inhabit 
shady places, and his opinion is that the simul¬ 
taneous existence of red and white spots aids trans¬ 
piration by producing an unequal absorption of heat. 
The white spots are produced by the presence of 
large air-spaces beneath the epidermis, the result being 
that the spots cool more slowly at nights and so 
receive less dew, and therefore render transpiration 
possible even at a low temperature. The paper con¬ 
tains some other observations which we need hardly 
note here. The reviewer of Stahl’s paper in the 
Botanische Zeitung calls it a model of biological 
investigation, and in its lavish employment of in¬ 
genious hypotheses it may at least be regarded as a 
type of many biological investigations. 
Another investigation which seems to throw more 
light upon the peculiarities of the distribution of 
anthocyan is one by Molisch. In working at antho- 
cyan, Molisch (1889) attempted to obtain a solu- 
