CHAPTEE VII. 



THE STRUCTURE OF THE LEAF. 



The leaf a machine Compared to an umbrella Ribs and vessels 

 compared to girders and water-pipes Leaf-skeletons Epi- 

 dermis Vascular system Mesophyll Continuity of tissues of 

 like kind. 



As already stated, it is not within the scope of the present 

 work to enter into the details of the anatomy and micro- 

 scopic structure of leaves, but since it will be necessary 

 to say something of the principal functions of these im- 

 portant organs, and since it would be impossible to under- 

 stand the actions and reactions which go on inside them, 

 without reference to the leading features of their internal 

 structure, it will be necessary to have a sketch at least of 

 the machinery concerned. 



For the leaf is, in effect, a complex piece of machinery, 

 the working of which may be compared generally with 

 that of many engines, though no artificial structure com- 

 pares with it in efficiency or delicacy of action, and the 

 comparison must always be understood with that qualifi- 

 cation. 



It has already been pointed out that the ordinary 

 green foliage-leaf is essentially a thin lamina of soft tissue 

 stretched on a framework of supporting fibres, much, in 



