276 Mr Philip Sewell on the [sess. lu. 



The Colouring Matters of Leaves and Flowers. 

 By Philip Sewell. 



(Read 8tli ilarch, 12th April, and 10th May 1888.) 



[The following paper was, for convenience, divided into three 

 parts, the first dealing with the physical and chemical properties 

 of this class of colours ; the second with colour changes ; the third 

 with the various hypotheses which, more or less recently, have 

 been put forward to account for colour phenomena. 



The paper is an expansion of one on Floral Colour, read in 

 December of last year to the Botanical Society.] 



Part I. 

 A. Physical Proijcrties. 



Their different physical characters were, naturally enough, 

 those that first attracted the attention of botanists who 

 wished to classify the various colours of plants. Many 

 workers, since the time of De Candolle, who divided plant- 

 colours into solid and fluid (xanthic and cyanic), have pointed 

 out the necessary imperfection of a purely physical classifica- 

 tion of them, and at the present time solubility, the appear- 

 ance of particular spectra, and, so far as can be ascertained, 

 chemical composition, all enter into account in any attempt 

 at a natural grouping together of colouring matters of 

 plants. 



If we inquire as to wliat is the nature of the difference 

 between so-called solid and fluid colours, we find that the 

 solid are associated with <a protoplasmic corpuscle of varying 

 size and shape, and may, therefore, be called by the better 

 name, used by Vines, "fixed" colours, Pringsheim states 

 that some of these protoplasmic corpuscles have in their 

 surface small pits, in which is mechanically retained the oily 

 or viscid coloured fluid — the chlorophyll or the etiolin, as 

 the case may be. The fluid colours are connnonly dissolved 

 in the cell-sap, although at times, as we shall see, they pass 

 into the cell-wall or into tlu! solid cell-coutcnts, or, and 

 this not uncommonly, occur crystallised within the cell. 



The fault of De Candolle's classification, which of course 

 was a ])urely arbitrary one, is clearly seen in this, that he 

 regarded yellow colours as solid colours distinctively, blue and 



