258 SMITH : 



would absorb those rays which would otherwise be absorbed 

 by and destroy the chlorophyll. It will be seen that to this 

 argument no adequate reply has yet been forthcoming. 



Meanwhile, Kerner (15), 1883, had carried on experiments in 

 the Alps on the growth of plants brought from lowland 

 districts. He found that of the varieties he transferred, those 

 grew best which had red colouring matter, while ordinary 

 green-leaved species did badly. He explained this by sup- 

 porting the screen theory, and supposed that those without 

 the red colouring matter suffered by the exposure to the 

 intense light of the higher Alpine regions. He interpreted 

 the red colour as a protection against the destruction of 

 the chlorophyll, and also against the oxidation of assimilated 

 products of the leaf. His experiments are of special impor- 

 tance, because they are constantly quoted, as we shall see, by 

 later writers on both sides of the controversy. 



Pick (23), 1883, brought forward the idea that the red 

 colouring matter w^as useful in furthering translocation, as it 

 screened from those rays which tend to dislocate the machinery 

 of translocation. His work has been adversely criticised by 

 Ewart, Stahl, and Overton, and it may be concluded that his 

 experiments were crude, although he collected many useful facts. 



Hassack (11), 1886, devoted the greater part of his paper to 

 an anatomical investigation into the position and distribution 

 of the coloured sap in coloured leaves. In his general conclu- 

 sions he supported the screen theory of the function of antho- 

 cyan, resting his argument on Kerner' s results with plants in 

 Alps and the general occurrence of red and of intenser colours 

 in plants much exposed to sunlight. Up to this point then, 

 when Engelmarm (6) in 1887 made his attack upon the screen 

 theory, most writers had favoured it. We now come to 

 Wiesner's (31) paper, 1894. He assumed that chlorophyll, 

 especially while developing, needed protection and supported 

 the screen theory of the function of anthocyan. This he did 

 from a consideration of the results of other researchers, 

 especially prominent among them being Kerner. He was 

 inclined, however, to minimise somewhat the protective effect 

 of anthocyan, and stated it to be only a link in a chain of 

 protective measures. 



