CHAPTER X. 

 LEAVES, THEIR FORM AND MOVEMENT. 



i. THE GROSS PARTS OF THE LEAF. 



120. 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 blade to the stem. The petiole is sometimes absent, 

 in which case the blade is attached directly to the stem. The 

 blade is the essential part of the leaf physiologically, and there- 



Fig. 66. 

 Leaf of hydrangea, showing blade and petiole. 



fore in all plants where the leaf performs its normal work (see 

 Chapter XII) the blade is usually present. 



121. 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 (figs. 68, 71). These are the 

 stipules. The stipules are either permanent and remain at- 

 tached to the petiole during the life of the leaf, as in the apple, 

 pea, etc., 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. 



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