CHAPTER IX. 

 LEAVES, THEIR FORM AND MOVEMENT. 



1. THE GROSS PARTS OF THE LEAF. 



115. Blade and petiole. The majority of leaves consist of 

 two rather distinct parts, the blade and the petiole. The blade 

 is the thin, expanded portion; the petiole is the stalk which 



attaches the leaf 

 to the stem. The 

 petiole is some- 

 times absent, in 

 which case the 

 blade is attached 

 Fig. 63. directly to the 



Leaf of hydrangea, showing blade and petiole. 



is the essential part of the leaf physiologically, and therefore in 

 all plants where the leaf performs its normal work (see Chapter 

 XI) the blade is usually present. 



116. Stipules. With many leaves there are also present 

 small or medium sized appendages which are attached one on 

 each side at the base of the petiole, or they are attached to the 

 stem at the junction of the petiole. These are the stipules. The 

 stipules are either permanent and remain attached to the petiole 

 during the life of the leaf, as in the apple, pea, etc. (figs. 65, 68), 

 or they fall away early, as in the elm. In the former case 

 they are usually green; in the latter they are often pale. The 

 stipules are sometimes quite large, and the two together enclose 

 the leaf in the bud, as in the tulip tree, and the point of attach- 

 ment of the two extends entirely around the stem. In the false 

 acacia the stipules are in the form of stout spines. 



117. Parts of the leaf in the Indian corn and grasses. 

 In the grasses the part of the leaf attached to the stem folds 



70 



