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- 



