CHAPTER XXVI 



LEAVES 



Structure of leaves. It is necessary to know some- 

 thing about the structure of leaves in order to under- 

 stand the method by which they carry on the processes 

 which make them such important parts of plants. You 

 already know that a leaf has a 

 broad part of green color, the 

 blade. Most leaves also have a 

 stem-like part, the petiole. Some- 

 times two leaf-like 

 parts, stipules, are 

 present at the base 

 of the petiole. The 

 blade may take al- 

 most any conceiv- 

 able shape, but it 

 is always strength- 

 ened by a frame- 

 work of tubes 



called veins. These veins are con- 

 tinuous with tubes passing through 

 the petiole and down through the 

 stem of the plant into the root. Veins 



200 



Petiole 



Fig. 76. Apple leaf, 

 net-veined. 



Fig. 77. Leaf 

 o f lily-of-the-. 

 valley, parallel- 

 veined. 



