INTERNAL TEMPERATURE OF LEAVES. 259 



Keeble ( 14) , 1895, in a paper dealing with the hanging foliage 

 of certain tropical trees also dealt with the question of the 

 function of anthocyan, since it was present in Amherstia 

 nobilis, the tree upon which most of his experiments were 

 made. He supported the protective function of anthocyan, 

 and performed an experiment tending to show that chlorophyll 

 in young leaves of Amherstia was to some extent destroyed 

 if fully exposed to sunlight, and therefore stood in need of a 

 protection. He. however, put anthocyan as a protection in a 

 somewhat minor position, because of the fact that it is not 

 universally distributed in plants in those positions in which the 

 exposed chlorophyll needs a protection. He thought it to be, 

 however, an eflficient protection in the somewhat limited 

 number of cases where it is present in such positions. He 

 obtained temperatures registered by thermometers placed both 

 above and below such red leaves and compared them with 

 those obtained with green leaves. From his somewhat rough 

 experiments he drew the novel conclusion, which has been 

 adversely criticized by later authors (Stahl, &c. ) , and is exactly 

 the opposite of the conclusion logically to be drawn from his 

 observations, that the red colour is a protection against too 

 great heating up of the leaf, i.e., that it ends to keep down the 

 temperature of the leaf. 



In 1896 8tahl (28) published a most important paper and 

 brought forward, in a long survey of the distribution and 

 structure of plants with coloured and variegated leaves, the 

 idea that the chief value of anthocyan was to raise the tem- 

 perature of leaves by absorption of the sun's rays. Tliis 

 favoured, he thought, in temperate and cold climates translo- 

 cation and in tropical chmates transpiration. He emphasized 

 the argument of Engelmann (6), which had been lost sight of by 

 later writers, that since anthocyan lets through just those rays 

 which are absorbed by the chlorophyll, its function cannot be 

 protective. His view of the screen theory is that while it 

 plausibly explains certain facts, chiefly of distribution, yet these 

 facts can be explained on his theory also, and that so far there 

 have been no decisive experiments made to settle the matter 

 between the two theories. The chief value of his paper is that 

 he supports his theory by experimental data, sho\^ing that it 



7(1)09 (34) 



