FLORAL COLOURS AND FIGMENTS, 



467 



the light passed by the soluble pigment, and little or none would reach 

 the surface again. The effect would be a dark neutral brown or black. 



I can recall but one instance of a blue dissolved pigment overlying 

 yellow particles in a flower. This condition may be produced artificially, 

 however, by placing a flower containing soluble red pigment overlying a 

 yellow in an atmosphere of ammonia. By this means the dissolved red 

 pigment becomes blue, and where the soluble pigment is in large quantity 

 the resultant colour effect is black ; where it is in slight concentration the 

 induced effect is green. 



I know also of one instance of a blue dissolved pigment overlying 

 a yellow pigment in solution. In this case, which will be described later, 

 the combined effect is green. 



It must not be forgotten that the extent to which selective absorption 

 takes place is dependent on the amount of pigment present. The 

 presence of solid particles of pigment which have separated out from a 

 saturated solution always greatly increases the absorption of light. And 

 in cases where pigment has separated from solution and formed com- 

 pounds with other cell constituents, such compounds being of a different 

 colour from the solution, nearly all the light may be absorbed, and a 

 black be produced. 



There is no instance among plants, so far as I am aware, such as is 

 frequently found in animals, of subjective colours produced by the inter- 

 ference of light in thin films, and without the presence of pigmented 

 substances. Nor is there any example in the plant world of pigmented 

 bodies "expanding with diffusion of pigment, and contracting with 

 intensification of tint, from yellow to orange^ or from orange or red to 

 brown or black," such as is to be found amongst fishes and other 

 animals.* 



Floral Pigments. 



So few of these pigments have been obtained in a state of purity, and 

 so little is known of their composition and constitution, that no classifica- 

 tion of them on a scientific basis is possible. Since, however, some 

 classification is necessary for orderly reference, it has usually been made 

 on their colour, and their solubility in water. In the present state of our 

 knowledge this is, perhaps, as good as any other. There are, therefore, 

 two main classes : — 



1. Those which are insoluble in water and in the cell-sap of plants. 



2. Those which are soluble in water and in the cell-sap of plants. 



1. Insoluble Floral Pigments. 



This class contains pigments which are always found contained in, or 

 which, at any rate, have been formed in, certain specialised bodies of a 

 proteid nature, of minute size, called plastids. In early life the plastid is 

 always colourless, and in some cases it remains so throughout life. Then 

 it is called a leucoplastid, and is more often to be found in the sub- 

 terranean parts of plants. The plastid may, however, develop a green 

 pigment and become a chloroplastid or chlorophyll corpuscle, and may 



* Bridge, Cambridge Natural History, Fishes, Ascidians, etc., p. 109. 



