CHAPTER XV. 



The Colouration of Plants. 



THE general structure of plants is so simple in comparison with 

 that of animals that our remarks upon this sub-kingdom need 

 only be short. 



With regard to leaves, especially such as are brightly coloured, 

 like the Begonias, Caladimus, Coleus, and Anoechtochilus, Plate XI., 

 the colour follows pretty closely the lines of structure. We have 

 border decoration, marking out the vein-pattern of the border ; the 

 veins are frequently the seat of vivid colour, and when decolour- 

 ation takes place, as in variegated plants, we find it running along 

 the interspaces of the veins. These facts are too patent to need 

 much illustration ; for our zonale geraniums, ribbon grasses, and 

 beautiful-leaved plants generally, are now so common that everyone 

 knows their character. When decay sets in, and oxidation gives 

 rise to the vivid hues of autumn, we find the tints taking structural 

 lines, as is well shown in dying vine and horse-chestnut leaves, Fig. 

 1, Plate XI. This shows us that there is a structural possibility of 

 acquiring regional colouration. 



We must remember, too, that the negative colouration of these 

 dying leaves is of very much the same character as the positive 

 colouration of flowers, for flowers are modified leaves, and their hues 

 are due to the oxidation of the valuable chlorophyll. 



In leaves the tendency of spots to elongate in the direction of the 

 leaf is very marked, as may be well seen in Begonia. Fig. 17, 

 drawn to illustrate another point, shows this partly. When leaves 

 are unsymmetrical, like the begonias, the pattern is unsymmetrical 

 also. 



Among parallel veined leaves we find parallel decoration. Thus, 



