SIGNIFICANCE OF ANTHOCYANIN. 483 



SIGXIFICANCE OK ANTHOCYANIN IN TUK TRANSPORTATIONS AND TRANS- 

 FOKMATIONS OF MATERIALS. AUTUMNAL COLOURING OF FOLIAGE. 



lu connection with the foregoing results of investigations into the transmission 

 of substances, the fact must be noted that those agents which take part in the 

 tninsfonnjitions of CiirbDhydrates and albuminous substances are to be found all 

 along the i-oad which these follow and not merely at the beginning and end of the 

 journey. Diastase, for example, is to be found everywhere along the strands of 

 cells forming the path of the transitory starch, and when these strands run near 

 the surface that colouring-matter called anthocyanin, a somewhat detailed descrip- 

 tion of which must be given, is also present. 



In many instances the route of the travelling substances can be recognized by 

 the naked eye, since it is coloured blue, violet, or red. Whether all these tints 

 actually originate from one colouring-matter, which is red, violet, or blue according 

 to the presence or absence of acids, has not been ascertained. The chemical 

 composition of colouring-matters is yet little known, and it is possible that at 

 present a whole group of them is collected together under the name anthocyanin. 

 It is a matter of indifierence with regard to the question in hand, as also is the 

 question as to the way in which anthocyanin originates in plants. It need only be 

 mentioned here that the statement according to which anthocyanin arises from the 

 chlorophyll-corpuscles present in young plant organs cannot be correct in all cases; 

 since this pigment occurs regularly in parasites entirely devoid of chlorophyll, in 

 the Balanophoreae, Rafflesiacefe, and Hydnoreaa, in the Toothwort, in Monotropa, 

 and numerous other plants destitute of green colour. In green-leaved plants 

 anthocyanin is most usually met with in places which have little chlorophyll, or 

 which have never possessed any, in flowers and fruits, along the ribs of leaves, and 

 principally in leaf-stalks and herbaceous stems. In hundreds of species belonging 

 to widely-differing families the leaf-veins and ribs, leaf-stalks and leaf-sheaths are 

 coloured violet, red, or blue, and this colouring is co-extensive with the vascular 

 bundles beneath them. 



It is difficult to say whether anthocyanin exercises a photochemical effect on the 

 travelling substances in the given paths, or whether it is only of use in that it 

 keeps back the light rays which would decompose the travelling materials. In 

 .support of the latter view we have the fact that anthocyanin is much more 

 abundantly deposited in paths exposed to the light than in those which arc shaded, 

 and that in shaded organs the same changes and transmissions of materials occur 

 as in those exposed to bright light, where the superficial cells are coloured with 

 anthocyanin, and where consequently the paths of the transmitted substances below 

 are to some extent screened. It is noticeable that plant organs which are very 

 thickly covered with hairs scarcely ever develop anthoc^'anin. From all this it may 

 be concluded that anthocyanin, when it appears in places directly illumined by light 

 rays, serves principally as a screen, i.e. as a protective agent or awning against 

 injurious light rays. 



