NATURAL COLOURS 430 



> CHAPTER XXX 



NATURAL COLOURS 



THE vegetation which clothes so large a part of the earth's sur- 

 face, though differing so much in form, height, structure, and 

 general character from the tropics to the limits of temperate 

 zones, agrees in one character, namely, the colour of the foliage 

 when young and active. This green colour extends to all except 

 the lichens which cover some rocks, the fungi, of which the repro- 

 ductive apparatus is alone conspicuous, and some few algae. 

 The green colour is in practically all cases due to the presence of 

 a substance named chlorophyll, literally the green of the leaf 

 (xAoo/oo? grass green, <pv\\ov a leaf). This is deposited in the 

 form of irregularly shaped granules contained within the cells 

 of the leaf and other green parts of a plant. By viewing under 

 the microscope a thin section of any such part it will be seen 

 that the chlorophyll grains are chiefly found in the cells which 

 lie just beneath the surface of the leaf. As a rule this substance 

 is only formed in the presence of daylight; and its production is 

 greatly accelerated by direct sunlight. When a plant is allowed 

 to grow in the dark the chlorophyll is suppressed and the result 

 is the familiar " blanching " which is commonly practised by 

 the gardener. The production of the green colouring matter is 

 intimately associated with the development of many character- 

 istic vegetable principles, such as essential oils, bitter and flavour- 

 ing substances, as may be noticed in the blanched stems of 

 celery, sea-kale, leek, etc. Its relation to the production of 

 starch is of the utmost importance in vegetable physiology, as 

 starch is usually first formed within the chlorophyll granules 

 and is probably formed by them or with their indispensable 

 assistance directly from atmospheric carbon dioxide. It appears 

 from experiments made by Pf effer long ago that when plants are 

 kept in an atmosphere entirely deprived of carbon dioxide they 

 form no starch, even in strong sunlight. 



It is not, however, in the explanation of how starch is pro- 

 duced in the plant nor in the origin of chlorophyll that advances 

 of special interest have been accomplished within recent years, 

 but in the practical solution of the question as to the composi- 

 tion and constitution of this green pigment. The problem is not 

 new to chemists. For the greater part of a century attempts 

 have been renewed many times to devise a method by which 



