MORPHOLOGY OF THE LEAF. 



93 



only, a double stipule is formed opposite to the leaf, as in the 

 Buttonwood. If they cohere by their inner margin, the double 

 stipule appears in the leaf axil, as in the Pond-weed (Potamo- 

 goton). The Ligide of the Grasses is generally regarded as a 

 double axillary stipule. The leaflets of compound leaves are 

 sometimes furnished with little stipules, called stipels. 



280. Inter-petiolar stipules occur in a few opposite-leaved 

 tribes, as the Galium tribe. Here we find them as mere bristles 

 in Diodia, while in Galium they look like the leaves, forming 

 whorls. Such whorls, if complete, will be apparently 6-leaved, 

 consisting of two true leaves and four stipules. But the adja- 

 cent stipules are often united, and the whorl becomes 4-leaved 



303, Leaf of Selinum, tripinnate, with sheathing petiole. 304, Leaf of Polygonum Pennsylvaniciim, 

 with its (o) odiren. 305, Culm of Grass, with joint (;), leaf (0, Hgule (s). 306, Leaf of Fear-tree, 

 with slender stipules. 



281. Stipules are often fugacious, existing as scales in the bud, 

 and falling when the leaves expand, or soon after, as in the 

 Magnolia and Tulip-tree. 



282. Nature of veins. The blade of the leaf consists of, 

 (1) the frame-work, and (2) the tissue commonly called the pa- 

 renchyma. The frame-work is made up of the branching vessels 

 of the footstalk, which are woody tubes pervading the paren- 

 chyma, and conveying nourishment to every part. Collectively, 

 these vessels are called veins, from the analogy of their functions. 

 VEXATION is a term denoting the manner in which the veins are 

 divided and distributed. The several organs of venation, differ- 

 ing from each other only in size and position, may be termed 

 the midvein, veins, veinlets, and veinulets. (The old terms, mid- 

 rib and nerves, being anatomically absurd, are here discarded.) 



