CHAPTER I. 



THE LEAF. 



The typical foliage-leaf Position and insertion Nodes and inter- 

 nodes Phyllotaxy Angular divergence Alternate and op- 

 posite leaves &c. Displacements Leaf-mosaic The leaf as 

 "a trap to catch a sunbeam " Examples of leaf-insertion. 



However difficult it may be to define a leaf so as to 

 exclude all things which are not morphologically leaves 

 and to retain all which are, it may be safely assumed that 

 the reader knows some common examples of foliage-leaves, 

 and it will be well to confine our remarks at first to these 

 only. 



The ordinary typical foliage-leaf, then, is a flattened 

 green expansion of tissues so displayed as to expose as 

 large an area as possible to the light and air. These 

 tissues are continuous with those of the stem, and present 

 the most various modifications in respect of position, 

 shape, size, texture, and other peculiarities which render 

 foliage so different. 



As regards position, the rule is that the leaf springs 

 direct from the shoot or from one of its branches, and it 

 is by the presence of leaves that we recognise shoots. The 

 spot where the leaf begins to leave the stem is termed 

 its insertion. The leaf-insertions may be close together, 



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