ORGANS OF GROWTH. 



27 



Leaves. (L. folium, G. phyllon.) 



Leaves are flat expansions common to most plants, 

 and are sometimes only in a very rudimental state, or 

 entirely wanting, as in the cactus family and other plants 

 called succulents. They vary from the eighth of an 

 inch to twenty and even thirty* feet in length, and in 

 form and size from a small needle to a complete circular 

 disc, from five to six feet in diameter, as in the Victoria 

 lily. They are either deciduous, that is, ripening and 

 falling to the ground in autumn, being reproduced in 

 the spring, or permanent for two or more years, as in 

 evergreen trees and shrubs. In Araucarias and others of 

 the fir family they are permanent for many years, only 

 losing their vitality with that of the branch or ramlet, as 

 explained under branches. 



Leaves perform an important part in the life of plants, 

 and in conjunction with the roots assimilate the difi'erent 

 substances absorbed in the sap. 



The structure of leaves is cellular, the cells containing 

 a matter called chlorophyll, which gives them their 

 colour. Although green is the normal tint, there are 

 many departures from it, as in red cabbage, the sombre 

 prince's feather, purple beech and perilla. Others again 

 have the brightest colours, as several species of caladium 

 and begonia ; several aroids are quite of a metallic hue. 

 When the colours are mixed, as in holly and aucuba, 

 they are called variegated ; some have lines or bars, as 

 the zebra plant ; others of the same genus have golden, 

 white and pink stripes ; and in the Indian shrub Grap- 

 tophyllum hortense, the variegation resembles caricature 



See index, Large Leaves. 



