Structure and Growth. 21 



under ordinary circumstances, found anywlicro else. Tlicy 

 occasionally, however, appear on other parts, when they aro 

 called (as when found on the roots) adventitious buds. It 

 is by means of the leaf-buds that a cutting is capable of pro- 

 ducing a new individual like that from which it was taken. 

 Leaf-buds are also capable, under fitting cir- 

 cumstances, of growing when separated from 

 the parent branch. In some cases they are 

 planted in the earth, when they put forth roots, 

 and thereby sustain an independent existence. 

 In others they are inserted below the bark 

 of a kindred species, ,and, forming new wood, 

 adhere to that on which they arc placed. 



The principal functions of the stem (aside 

 from its continual multiplication of itself by buds. 



means of buds) are the su[)port of the leaves and the convey- 

 ance and distribution of the sap. In trees, the sap or crude 

 food procured by the roots rises principally through the newer 

 wood ; but the assimilated sap returns from the leaves in tho 

 newest bark, or liher, whence it is horizontally diffused, through 

 the medullary rays, into the sai)-wood and other living parts. 

 It is in the bark, therefore, and not in the wood, that we must 

 look for the proper juices of a plant. 



IV.— LEAVES. 



A leaf, as defined by Dr. Lindley, is an appendage of the 

 stem of a plant having one or more leaf-buds in its axil, or 

 point of union with the stem. In some cases no leaf-buds aro 

 visible, but they are present, nevertheless, although latent, and 

 may be developed by favorable conditions. 



A complete leaf consists of the lamina, or blade, and tho 

 petiole, or leaf-stalk. In some leaves the petiole is wanting, 

 the lamina resting immediately upon the stem, and in others 

 there is no proper blade, the whole organ being cylindrical or 

 stalk-like. 



Considered in reference to their structure, it may bo said 



