THE LEAVES. 73 



and then diverge at some distance from the stem, forming the 

 expanded lamina of the leaf. The points of the stem from 

 which these fasciculi have issued are apparent on the scars left 

 by the fallen leaf stalks in the form of round dots, of a uniform 

 number and arrangement in each species of plant. Thus in 

 the apple, the pear, and the peach, the leaf is attached to the 

 stem by three fasciculi or bundles of woody fibre, and three 

 round dots may be distinctly seen on the leaf scar ; and in the 

 horse-chestnut, from five to seven dots are visible on the leaf 

 scar, the number of fasciculi passing out of the stem and 

 uniting in the petiole being the same as the number of the 

 leaflets. 



The vascular or woody system which passes out of the 

 stem into the leaf is clearly designed to give to it the needful 

 strength and support, as well as to convey the sap to be aerated 

 in the leaf. This part of the leaf evidently constitutes its 

 framework or skeleton. The vascular and woody system in 

 exogenous leaves, as for example, that of the Cornus florida, or 

 Flowering dogwood, consists of a distinct midrib or keel, and 

 less elevated ribs, (costse,} which proceed from the sides of the 

 midrib and take a curvilinear direction to the margin and 

 apex of the leaf. On closer investigation the costee are seen 

 to communicate with each other by means of small transverse 

 fibres, which again branch and subdivide in various ways, the 

 last ramification or branchlets running together or anastomosing 

 amongst themselves, and the whole forming a delicate and 

 beautiful network. 



Seen through the microscope, this vascular framework is found 

 to consist of woody fibre enclosing spiral vessels. This is its 

 constitution, from the main fasciculus or bundle of woody fibre 

 called the midrib or keel of the leaf, through the several fasci- 



