vin] THE SIGNIFICANCE OF ANTHOCYANINS 141 



if any, is gained by the plant in this way is quite another question, 

 but it is well to have this physical effect definitely established." 



When we review the work on the subj ect of the uses of anthocyanin, 

 we find it singularly unconvincing in any direction. In favour of the 

 light-screen hypothesis, there is undoubtedly a greater development of 

 anthocyanin in sun-exposed leaves than in leaves of the same plant in 

 the shade; and, conversely, in red-leaved plants like the Blood Hazel 

 and Copper Beech, a lack of colour in leaves which happen to be 

 shaded. But, on the other hand, Kerner's experiments on Satureja 

 and Linum are not very convincing, since so many factors might account 

 -for the unhealthiness of the Flax plants. And again, even if Prings- 

 heim's red screen were protective to chlorophyll, it consisted of iodine 

 in carbon disulphide which has a different absorption spectrum from 

 anthocyanin. Moreover, Engelmann's analyses seem to prove that the 

 anthocyanin only absorbs those rays which pass through chlorophyll, 

 and an effective screen would be one with a similar absorption spectrum 

 to chlorophyll itself. As regards Stahl's hypothesis, it is certainly 

 supported by a definite piece of evidence, viz. that the temperature of 

 red leaves is higher than that of green. Also, there are without doubt 

 a number of shade plants which do possess anthocyanin to a considerable 

 extent. Yet it is difficult to find a hypothesis which would fit all cases 

 of anthocyanin distribution without reduction to absurdity. The 

 pigment is produced, of necessity, in tissues where the conditions are 

 such that the chemical reactions leading to anthocyanin formation 

 are bound to take place. For the time being we may safely say that 

 it has not been satisfactorily determined in any one case whether its 

 development is either an advantage or a disadvantage to the plant. 



