460 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



some of the light being scattered if there be solid particles present— and 

 meets the inner walls of the cells. Here some of it is reflected and passes 

 out of the cell again into the air ; the remainder passes into the subjacent 

 cells and there goes through the same course as in the epidermis. The 

 consequence is that the light coming from the petal of a flower, and by 

 which we view it, has passed through the walls and contents of one, two, 

 or more layers of cells before it reaches our eyes. The flower appears 

 white, although made up of transparent, colourless elements, for the same 

 reason as the mass of bubbles which constitute foam appears white, 

 although made up of water, because we view it by the light which, 

 impinging upon it, is scattered and thrown back by the numerous 

 reflecting surfaces it meets. Whilst the white flower absorbs white light, 

 so that in sufficient thickness it would be opaque, it exercises no sensible 

 selective absorption. 



Now consider the case of a flower which has a dissolved red pigment 

 in its cells. The white light incident on its outer surface is partly reflected 

 there as white light. As this is invariably the case, the colour of no flower 

 can be saturated or pure. The rest of the light passes into the coloured 

 cell-sap, where a portion of it is selectively absorbed, and the remainder, 

 reflected from the various cell-walls it meets, or scattered by the solid 

 particles in the cells, emerges from the surface and gives its hue to the 

 flower. In this case it would be an unsaturated or impure red. 



Next consider the colour effect when two pigments are present in the 

 cells, and take as examples cases where a yellow pigment in solid 

 particles {a) underlies, (b) is evenly mixed with a dissolved red pigment. 



(a) Some white light is scattered from the outer surface. The 

 remainder enters the red cell-sap, suffers selective absorption, and is 

 deprived chiefly of its violet, blue, and green constituents, and even of the 

 yellow and orange if the solution be very strong indeed — the character and 

 amount of the light absorbed depending on the strength or depth of the 

 red solution. The residue, as a rule consisting chiefly of red, orange, and 

 some yellow light, then meets the yellow particles, where further absorption 

 of nearly the same constituents takes place with some of the red. The 

 light reflected out of the cells then consists of red, orange, and yellow, 

 not, however, in the same proportions as they exist in white light, 

 together with some white light, and the resultant colour effect varies 

 from orange to red-brown according to the nature and strength of the 

 pigments. 



(b) If the yellow particles be evenly mingled with the dissolved red 

 pigment, more yellow light will be reflected out of the cells by the 

 particles nearer the surface, and the colour effect will be a more decided 

 orange. It will also be more luminous. 



Should the overlying dissolved pigment be of a crimson, purple, 

 violet, or any other colour compounded of red and blue, then, in addition 

 to some absorption at both ends of the spectrum, there will be a broad 

 absorption band in the orange and yellow. The colour effect of such a 

 solution of pigment overlying solid yellow particles would vary according 

 to the strength of the solution, but would be in general a dark chocolate. 



Should the pigmented particles be green chlorophyll corpuscles under- 

 lying the red solution, then the chlorophyll would absorb all, or nearly all, 



