CHAPTER VIII 



THE SIGNIFICANCE OF ANTHOCYANINS 



Biological significance. 



The function of anthocyanins in rendering the corolla, perianth, 

 bracts and other parts of the inflorescence attractive to insects may be 

 regarded as their biological significance ; so also the function of making 

 ripe fruits conspicuous to birds. Neither of these subjects is dealt with 

 in the present volume, but references are given to the work of Knuth 

 (426), Focke (423) and others, from which further information can be 

 obtained. 



Physiological significance. 



Several physiological functions have been assigned to anthocyanins 

 but, broadly speaking, they fall into three classes. Though each hypo- 

 thesis has been closely criticised by the various investigators of the 

 problem, the final issue is far from being complete and satisfactory. 

 The three main ideas are : 



1. That of shielding the chloroplastids from too intense insolation; 

 this is known as the 'light-screen' hypothesis. In slightly different 

 forms it has been advocated by Kerner, Kny, Wiesner, Keeble and 

 Ewart. 



2. That of assisting the action of diastase by screening it from 

 deleterious rays, and thereby facilitating the hydrolysis of starch and 

 subsequently translocation. This view has been mainly supported by 

 Pick, and Koning & Heinsius. 



3. That of absorbing certain light rays and converting them into 

 heat. Though the conception of anthocyanin as a medium for raising 

 the temperature of tissues was due to earlier writers, notably Comes 

 and Kerner, yet it was Stahl who first regarded this property as a valuable 

 asset in assisting transpiration; he also considered other processes of 



