STIPULES. 175 



great number of plants ; but their presence or absence is usually 

 uniform throughout each natural order. They commonly have the 

 texture, color, and venation of leaves, and are subject to similar 

 modifications. Like leaves, they are sometimes membranaceous 

 or scale-like, and sometimes transformed into spines, &c. ; and they 

 have also a strong tendency to cohere with each other, or with the 

 base of the petiole. Thus, in the Clover, the Strawberry, and the 

 Rose (Fig. 215), a stipule adheres to each side of the base of the 

 petiole ; in the Plane-tree, they are free from the petiole, but co- 

 here by their outer margins, so as to form an apparently single 

 stipule opposite the leaf. In other cases, both margins are united, 

 forming a sheath around the stem, just above the leaf : these are 

 called intrafoliaceous stipules, or, when membranaceous, as in Po- 

 lygonum (see Ord. Polygonacese), they have been termed ochrece. 

 When opposite leaves have stipules, which is not very common, 

 they usually occupy the space between the petioles on each side, 

 and are termed interpetiolar. The stipules of each leaf (one on 

 each side), being thus placed in contact, frequently unite, so as to 

 form apparently but a single pair of stipules for each pair of 

 leaves ; instances of which are very common in the order Ru- 

 biacese. 



305. When leaves are furnished with stipules, they are said to 

 be stipulate : when destitute of these appendages, exstipulate. 

 They are sometimes present in young leaves only ; as in the 

 Beech, the Fig, and the Magnolia (Fig. 130, 131), where they 

 form the covering of the buds, but fall away as these expand. 



306. The leaflets of compound leaves are sometimes provided 

 with small stipules (stipelles) of their own, as in the Bean (Fig. 

 221) ; when they are said to be stipellate. 



SECT. III. THE DEATH AND FALL OF THE LEAVES ; EXHALA- 

 TION, ETC. 



307. While the axis, or portion of each phyton that belongs to 

 the stem, is permanent during the life of the individual plant, the 

 leaf lasts only for a limited period, and is thrown off, or perishes 

 and decays, after having fulfilled its temporary office. 



308. Duration Of Leaves, In view of their duration, leaves are 

 called fugacious, when they fall off soon after their first appear- 

 ance ; deciduous, when they last only for a single season ; and 



