vi] INFLUENCING THE FORMATION OF ANTHOCYANINS 83 



the stems and petioles but not in the leaves. Ex. Ceanothus azureus, 

 Catalpa bignonioides. 



(c) Those in which pigment never appeared as a result of decorti- 

 cation. Ex. Rhodotypos kerrioides, Robinia Pseudacacia, Pinus excelsa. 



The time elapsing before the appearance of pigment also varied 

 considerably. In addition it was noted, as would be expected, that no 

 pigment appeared on decortication in albino varieties, although the 

 coloured type might produce abundant pigment under similar treat- 

 ment. 



(2) Injuries brought about by insects present no points of special 

 interest but may be regarded rather as cases of (1). Frequently the 

 midrib or petiole is partly eaten away, and reddening occurs on the 

 distal side ; or holes are eaten in the lamina, and red blotches are formed 

 in their vicinity. Mirande (362) has observed that excursions of leaf- 

 boring larvae in leaves of Galeopsis Tetrahit result in the production of 

 anthocyanin. Under this heading also may be included the develop- 

 ment of anthocyanin in or near galls. For details and examples the 

 works of Hieronymus (314), Kiistenmacher (326), Kiister (350) and 

 Guttenburg (353) may be consulted. 



(3) It is frequently found that the pathological conditions called 

 forth by the attacks of Fungi are accompanied by abnormal develop- 

 ment of authocyanin. In leaves of Tussilago, for instance, infected by 

 Puccinia a circular band of anthocyanin often appears surrounding the 

 aecidium spots. Other references to this matter may be looked for in 

 the works of Sorauer (304), Tubeuf (329), Liidi (342) and Rostrup (345). 



There is little doubt that, in the above cases of injury and decorti- 

 cation, the formation of pigment is directly connected with an inter- 

 ference with the translocation current. Injury to the living tissues of 

 the conducting system of the veins, midrib or petiole of the leaf, or 

 of corresponding tissue in the stem, leads to an accumulation of synthetic 

 products in the leaves. Of such products several authors Mirande 

 (365), Combes (207) have maintained that it is the carbohydrates and 

 glucosides which most influence the formation of anthocyanin, and 

 Combes has shown by analyses that leaves reddened by decortication 

 contain a higher percentage of sugars and glucosides. It seems likely 

 also that parasitic growths may interfere with the progress of the 

 translocation current through the small veins of the leaf, thereby causing 

 congested areas to arise in which the sugar contents are above normal. 

 But it is conceivable that the pathological condition resultant on fungal 

 attacks may be the direct cause, in some way, of pigment formation. 



62 



