110 STRUCTURAL BOTANY. [93, 94. 



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 con- 

 sists of, (1) the frame-work, and (2) the tissue com- 

 monly called the parenchyma. The frame-work is 

 made up of the branching vessels of the footstalk, 

 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. VENATION is the division and distribu- 

 tion of the veins. The several organs of venation, 

 differing from each other only in size and position, 

 may be termed the midvein, veins, veinlets, and veinu- 

 lets. (The old terms, midrib and nerves, being ana- 

 tomically absurd, are here discarded.) 



283. The Midvein is the principal axis of the vena- 

 tion, or prolongation of the petiole, running directly 

 through the lamina, from base to apex, as seen in the 

 leaf of the Oak or Birch. If there be several similar 

 divisions of the petiole, radiating from the base of the 

 leaf, they are appropriately termed Veins ; and the leaf 

 is said to be three-veined, five-veined, as in Maple. 

 The primary branches sent off from the midvein or 

 the veins we may term the Veinlets, and the second- 

 ary branches, or those sent off from the veinlets, are 

 the Veinulets. These also branch and subdivide until 

 they become too small to be seen. 



284. Botanists distinguish three modes of venation, 

 which are in general characteristic of three Grand 

 Divisions of the Vegetable Kingdom viz.: 



Reticulate or Net-veined, as in the DICOTYLEDONS 

 (called also EXOGENS). This kind of venation is char- 



