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A TEXTBOOK OF THEORETICAL BOTANY 



greater vigour of growth. The size of leaf steadily diminishes with age, 

 although, as we have remarked, the range of such individual variation is not 

 great. It has been remarked that the size of the meshes, in leaves with a 

 network of veins, likewise diminishes with age, this being one of the few points 

 in which plants show a distinct morphological change due to senescence. 



%0 



B 



I 



D E F 



Fig. 940. — Some common forms of Compound leaves. A, Pinnate ; Onohrychis. B, Bipinnate ; 

 Acacia. C, Tripinnate ; Anthrisciis. D, Ternate ; Choisya. E, Biternate ; Aqidlegia. 

 F, Digitate ; Lupinus. 



On the other hand, the variation of size between different species is 

 immense. Putting on one side the numerous cases of leaves which are reduced 

 to scales, many of which have been diminished almost to the vanishing point, 

 and considering only green foliage leaves, the largest known leaves are many 

 thousand times the size of the smallest. These differences are to some extent 

 related to the conditions of the environment, for larger leaves are usually 

 capable of a greater evaporation of water than small ones, in proportion to 

 their greater surface. Raunkaier has devised an ecological classification of 



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