100 THE STEM. 



or spire-shaped trees ; the second, to rounded or spreading forms. 

 As stems extend upward and evolve new branches, those near the 

 base, being overshadowed, are apt to perish, and thus the trunk be- 

 comes naked below. This is well seen in the excurrent trunks of. 

 Firs and Pines, which, when grown in forest, seem to have been 

 branchless for a great height. But tlio knots in the centre of the 

 trunk are the bases of branches, which have long since perished, 

 and have been covered with a great number of annual layers of 

 wood, forming the clear stuff of the trunk. 



171. Definite and Indefinite Annual Growth of Branches. In the 



larger number of our trees and shrubs, especially those with scaly 

 buds, the whole year's growth is either already laid down rudi- 

 mentally in the bud (159), or else is early formed, and the develop- 

 ment is completed long before the end of summer ; when the shoot is 

 crowned with a vigorous terminal bud, as in the Horsechestnut (Fig. 

 153) and Magnolia (Fig. 155), or with the uppermost axillary buds, 

 as in the Lilac (Fig. 154) and Elm. Such definite shoots do not 

 die down at all the following winter, but grow on directly, the next 

 spring, from these terminal or upper buds, which are generally more 

 vigorous than those lower down. In other cases, on the contrary, 

 the branches gi'ow onward indefinitely through the whole summer, 

 or until arrested by the cold of autumn : the}-^ mature no buds at or 

 near their summit ; or at least the lower and older axillary buds 

 are more vigorous, and alone develop into branches the next spring; 

 the later-formed upper portion most commonly perishing from • the 

 apex downward for a certain length in the winter. The Eose and 

 Raspberry, and among trees the Sumac and Honey Locust, are 

 good illustrations of this sort ; and so are most perennial herbs, 

 their stems dyijig down to or beneath the surface of the ground, 

 where the persistent base is charged with vigorous buds, well j^ro- 

 tected by the ground, for the next year's vegetation. 



172. Propagation from Buds. Buds, being, as it were, new indi- 

 viduals springing from the original stem, may be removed and 

 attached to other parts of the parent trunk, or to that of another 

 individual of the same, or even of a different, but nearly related 

 species, where they will grow equally well. This is directly accom- 

 plished in the operation of hudding. In ingrafting, the bud is 

 transferred, along with a portion of the shoot on which it grew. 

 Moreover, as the cut end of such shoots, when buried in moist and 

 warm soil, will commonly, under due care, send out adventitious 



