52 



OF THE VEINS. 



250. INTER-PETIOLAR STIPULES occur in a few opposite leaved tribes, as the Ga- 

 lium 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 appar- 

 ently 6-leaved, consisting of two true leaves and four stipules. But the adjacent 

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



102 103 104 106 



102, Leaf of Conioselinum, tripinnate, with sheathing petiole. 103, Leaf of Polygonum Penn- 

 sylvanicum, with its (o) ochrea. 104, Culm of grass, with joint (j), leaf (1) ligule (). 105, Leaf 

 of pear-tree, with slender stipules. 



251. THE LIGULE of grasses is generally regarded as a double axil- 

 lary stipule. The leaflets of compound leaves are sometimes furnished 

 with little stipules, called stipels. 



252. STIPULES ARE OFTEN FUGACIOUS, existing as scales in the bud r 

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

 and tulip-tree. 



OF THE VEINS. 



253. LEAVES, SIMPLE AND COMPOUND. A leaf is simple when its 

 blade consists of a single piece, however cut, cleft or divided ; and com- 

 pound when it consists of several distinct blades, supported by as man) 

 branches of a compound petiole. 



254. NATURE OF VEINS. The blade of the leaf consists of, (1) the 

 frame-wovk, and (2) the tissue commonly called the parenchyma. The 

 frame-work is made up of the branching vessels of the foot-stalk, which 

 are woody tubes pervading the parenchyma, and conveying nourishment 

 to every part. Collectively, these vessels are called veins, from the 

 analogy of their functions. 



255. VENATION is a term denoting the manner in which the veins 

 are divided and distributed. The several organs of venation, differing 

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

 veins, veinlets and veinulets. (The old terms, midrib and nerves, being 

 anatomically absurd, are here discarded). 



256. THE MIDVEIN is the principal axis of the venation, or prolong- 

 ation of the petiole, running directly through the lamina, from base to 



