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CHAPTER XV. 



OF LEAVES, THEIR SITUATIONS, INSERTIONS, SCJR- 

 PACES, AND VARIOUS FORMS. 



Folium, the Leaf, is a very general, but not univer- 

 sal, organ of vegetables, of an expanded form, pre- 

 senting a much greater surface to the atmosphere than 

 all the other parts of the plant together. Its colour is 

 almost universally green, its internal substance pulpy 

 and vascular, sometimes very succulent, and its upper 

 and under surfaces commonly differ in hue, as well as 

 in kind or degree of roughness. 



Leaves are eminently ornamental to plants from 

 their pleasing colour, and the infinite variety as well as 

 eleii^ance of their forms. Their many eeconomical uses 

 to mankind, and the importance they hold in the scale 

 of nature as furnishing food to the brute creation, are 

 subjects foreign to our present purpose, aiid need not 

 here be insisted upon. Their essential importance to 

 the plant which bears them, and the curious functions 

 by which they contribute to its health and increase, 

 will presently be detailed a-t length. We shall first 

 explain their different situations, insertions, forms, and 

 surfaces, which are of the greatest possible use in sy- 

 stematical botany. 



The leaves are wanting in many plants, called for 



