148 On the Formation of Anthoci/anin 



hydrates varies, being sometimes greater in one, sometimes in the 

 other. 



Since the concentration of both gliicosides and sugars is greater in 

 the red leaves, it is reasonable to interpret the pigment formation as 

 being due to accumulation of gliicosides, in which case the reaction 



Glucoside + water — *- sugar + chromogen 



would give rise to more free sugar (apart from other causes) in the red 

 than in the green leaf from whicii the glucosides are continually 

 removed, so that the concentration of glucoside is lowered 



Sugar + chromogen — ♦- glucoside + water. 



Kraus(6) has also shown that red autumnal leaves contain more 

 aromatic substances than normal red leaves. 



Results, however, which are more convincing than these just stated, 

 are those connected with the phenomenon of reddening produced by 

 injury. Instances have already been quoted of pigment formation due 

 to injury to the cortical tissues of the midrib and petiole or to the 

 removal of a portion of the midrib or main veins of a leaf. According 

 to Kraus(6) the path taken by aromatic substances in translocation is 

 the vascular system of the leaf, but whether by the phloem or the 

 surrounding parenchyma is not stated. In any case injury to the 

 vascular system of the leaf or the living tissues of the petiole or stem 

 would involve an accumulation of glucosides in the parts distal to the 

 point of injury. It has been recently suggested by Mangham(8) that 

 the sugars travel from the leaf by the phloem. If such is the case, the 

 injury may also lead to accumulation of sugars and hence indirectly to 

 more glucoside. 



Combes(3) has shown that decortication in spp. of Spiraea induces 

 reddening of the leaves above the point of operation. A similar obser- 

 vation has been made by Kraus for Cornus alba, and I have myself 

 observed a similar result following upon decortication in Ribes Grossu- 

 laria and a species of Salix. 



Combes (3) has shown by analysis that thei-e is a large increase of 

 both glucosides and sugars in the leaves of Spiraea which had reddened 

 as a result of decortication. 



The following are the numbers given : — 



Insoluble 

 Sugars Dextrins Glucosides Carbohydrates 



Spiraea paniculata green 2-21 1-Ul 1'64 10'75 



red 4-2G -92 6-15 26-58 



