458 M. Wheldale. 



Pigmentation in Flowering Plants. 



To the casual observer the range of colouring- exhibited by 

 flowering plants suggests the existence of an almost infinite variety 

 of pigments. Yet, apart from chlorophyll, and other allied substances 

 in the green colouring matter of foliage leaves, these bodies have 

 received but scanty attention. The majority of botanists have been 

 satisfied with such a classification as the microscope provides. This 

 method enables us at once to differentiate between pigments soluble 

 in the cell -sap, permeating the cell (anthocyanin), and pigments bound 

 up with the structure of specialised protoplasmic bodies distributed 

 through the protoplasm (plastids). Flower colour may be due to 

 representatives of eithei' one or both oi these classes. 



From the plant physiologist and the biochemist we gain further 

 information, namely, that the two classes are not interdependent; 

 that the colouring matters, moreover, of each class are represented 

 by organic bodies of different chemical nature and are products ot 

 different spheres of metabolic activity. Those constituting the soluble 

 class are, in all probability, members of the aromatic benzene group 

 and contain the elements carbon, hydrogen and oxj-gen. On the other 

 hand, the plastids, to which many yellow and orange flowers owe 

 their colour, are undoubtedly derived from green chloroplastids in 

 metamorphosis of foliage leaves. Of the nature of the plastid pig- 

 ments, very little is know^n, but such knowledge as we have indicates 

 that they may be ranked as hydrocarbons and if this be so, the 

 elements carbon and hydrogen are alone essential to their composition. 



For the present we are not concerned with plastid pigments; 

 for us the centre of interest lies with those bodies, which,, in solution 

 in the cell-sap, give the red, purple and blue colours to flowers, fruit 

 and in many cases also to stems and leaves. 



As I have already stated, the general term — anthocyanin — 

 has been used indiscriminately for all such forms of soluble colouring 

 matter. A few isolated attempts at differentiation and classification 

 have been made, it is true, from time to time by various investigators, 

 foremost among whom may be mentioned Weigert, Wiesner, 

 Overton and Gräfe. But the outcome of these efforts has not as 

 yet been very far-reaching. 



There can be little doubt that, as a class, many of these soluble 

 pigments closely resemble each other in general properties and 

 characteristics; yet, in my belief, chemical analysis, combined with 

 exact knowledge of the genetics of flower-colour, will go very far 

 towards proving that there are many constitutionally different forms 

 of anthocyanin and even, quite conceivably, a specific form for each 



