1887-88.] Colouring Matters of Leaves and Flowers. 277 



red as fluid distinctively. Hence, wlien it was recognised 

 that yellow commonly exists as a fluid colour, and that red, 

 and even blue, are at times attached to solid bodies, some other 

 more natural arrangement was required. The real relation- 

 ship of the colours is brought out in the assertion of Schimper 

 (in 1885) that, in the different stages of developing colour- 

 corpuscles, the^-e may be found all shades from pale yellow, or 

 green, to brilliant carmine ; whilst at the same time there is 

 transition of form of the retaining corpuscle. " The colouring 

 matters of leaf and flower affect a series of states connected 

 with and passing into each other," says Bonnier. We have 

 to think of evolution among coloured products in the cell ; 

 of the yellow of etiolin, as indicated fully in Vines' Lectures 

 on Physiology, becoming transformed into the green of chloro- 

 phyll ; or, on decomposition, passmg into yellow or red, 

 either retained by the corpuscle of protoplasm ; or, most 

 commonly passing (the yellow as xanthophyll) into the cell- 

 sap. We come, indeed, to regard the fixation of colouring 

 matters as a sign of specialisation — that is, of a division of 

 labour by the protoplasm of the cell. Amongst the lowest 

 Cryptogams it is present as a viscid fluid distributed through- 

 out the whole of the homogeneous protoplasm of the cell ; 

 amongst the Diatomaceae, or as in Spirogyra amongst fila- 

 mentous Algffi, it is present as bands in the protoplasm 

 lining the interior of the cell-wall. Its association in the 

 higher plants with the numerous distinct corpuscles, capable 

 of being moved in the cell by the investing layer of proto- 

 plasm, is a clear case of differentiation ; the corpuscles are 

 isolated as the special portions of the protoplasm which effect 

 the synthetic formation of carbohydrates. 



The development of the chlorophyll and of its corpuscle 

 (the chloroplast) has of late years, mainly through the ob- 

 servations of Schimper and Meyer, been very distinctly 

 followed. The chloroplasts arise from colourless plastids, 

 which have been traced in all young meristem, and even in 

 the embryo-sac of various plants ; they divide directly, and, 

 at maturity, a yellow colouring matter, etiolin, appears as the 

 result of the reduction of part of the protoplasm of the 

 corpuscle. It is this etiolin which on exposure to light may 

 become green. 



It is interesting to notice, that a starch-grain in the cor- 



TRANS. BOT. SOC. VOL. XVII. T 



