26 CHEMISTRY OF PLANTS. 



Chlorophyll is composed of a white wax-like substance ( 9.), and a pe- 

 culiar green colouring matter. Of the first substance it contains more if 

 the first removal of the green parts is effected by ether. The fine green 

 colouring matter originates almost universally under the immediate 

 action of light, which presupposes that there must be universally diffused 

 amongst plants some substance a colourless chlorophyll, the first form 

 of the pure colouring matter, and which is easily decomposed under the 

 influence of light. To the products of this decomposition belong espe- 

 cially a yellow, a blue, and a blackish colouring matter ; and under some 

 circumstances, according to Mulder, wax (?) also appears. The yellow 

 leaves in autumn contain proportionately more wax than the green leaves 

 of summer, the rind of the yellow ripe fruits more than the green rinds 

 of unripe fruits; but in both, starch, or its equivalent, inulin, is found 

 more abundantly earlier than later. The only analysis of this substance 

 hitherto made is the unsatisfactory one of Mulder, CIS H9 N2 O8, 

 which makes it a nitrogenous body, and which could not be formed out of 

 starch alone. Meyen's defence of this view (Physiologic, bd. i. p. 193.) 

 is a mere fiction. On the other hand, we know that, simultaneously with 

 the origin of every plant-cell, protein and protein-compounds appear, 

 and that these substances, at least, never fail to be present in the parts of 

 plants about to become green. It seems, therefore, more reasonable to 

 look for the origin of chlorophyll from protein. Chlorophyll also appears 

 very closely related with the colouring matter of indigo found in the 

 green leaves of the species of Indigofera, of Polygonum tinctorium, the 

 Isatis tinctoria, &c. The formula of blue indigo is C 16 H5 N2 O2; 

 of white (deoxidized) indigo, C16 H6 N2 O2. Pure chlorophyll is 

 soluble in hydrochloric acid, sulphuric acid, and the alkalies, with a 

 green colour ; it is soluble in ether and alcohol, but insoluble in water. 

 Exposed to the action of light, or treated with hydrogen in statu nascenti, 

 it is decolorised. 



The various shades of green of the organs of plants depend upon very 

 different causes : partly upon the nature of the chlorophyll, whether it is 

 pure or more or less mixed with the yellow, blue, and black products of 

 its decomposition ; partly upon the quantity of chlorophyll in individual 

 cells ; partly on the thicker or looser arrangement of these cells, which is 

 evident on the under sides of leaves, which are always of a fainter and 

 lighter green, depending on the intercellular spaces which are there 

 present, and which, reflecting the light white, mixes with and diminishes 

 the intensity of the green. Variegated leaves are produced in one of two 

 ways. First, the single groups of cells contain only the yellow product 

 of the decomposition of the chlorophyll, as in the Phalaris arundinacea 

 picta, a variety which appears on a dry soil, but disappears on a moist 

 one; or in the variegated varieties of the common holly (Ilex Aquifoliuni"). 

 Secondly, the epidermis separates itself from the cells lying under it in 

 particular places ; and the layer of air lying between them appears as a 

 bright silvery spot, as in Begonia argyrostigma, Silybum marianum, and 

 other plants. In the last place, the green colour of plants may be yet 

 considerably modified through the greater or less secretion of wax upon 

 the surface, which in some cases forms a layer of small silvery scales, 

 which appear almost snow-white, as in Elymus arenarius. 



2. Vegetable Colours. Of these we know at present very little. They 

 may be generally divided into soluble and insoluble. The last are found 

 in the cells of plants in the form of globules of a yellow (Fritillaria 

 imperialist red, and seldom of a blue colour ( Strelitzia farinosa) ; they 



