CHARACTERISTICS AND GROWTH. 49 



evolution of a terminal bud, or by some upper strong bud which 

 equally becomes a leader, forming an undivided main trunk, 

 *from which lateral branches proceed ; as in most Fir-trees. 

 Such a trunk is said to be excurrent. In other cases, the main 

 stem is arrested, sooner or later, either by flowering, by the 

 failure of the terminal shoot, or by the more vigorous develop- 

 ment of some of the lateral buds ; and thus the trunk is dissolved 

 into branches, or is deliquescent, as in the White Elm and most of 

 our deciduous-leaved trees. The first naturally gives rise to coni- 

 cal 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 becomes naked below. This strikingly occurs in the 

 excurrent trunks of Firs and Pines, grown in forest, which seem 

 to have been branchless to a great height. But the knots in 

 the centre of the wood 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 o f the trunk. 



87. Definite and Indefinite Annual Growth of Branches. In 

 many of our trees and shrubs, especially those with scaly buds, 

 the whole year's growth (except on certain vigorous shoots) is 

 either already laid down rudunentally in the bud, or else is early 

 formed, and the development is completed long before the end 

 of summer ; when the shoot is crowned with a vigorous terminal 

 bud, as in the Horsechestnut (Fig. 85) and Magnolia (Fig. 81), 

 or with the uppermost axillary buds, as in the Lilac (Fig. 86) 

 and Elm. Such definite shoots do not die down at all the follow- 

 ing 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 

 grow onward indefinitely, until arrested by the cold of autumn : 

 the buds at or near their summit are consequently young and 

 miniatured, 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 

 Rose and Raspberry, and among trees the Sumac and Honey- 

 Locust, are good illustrations of this sort ; and so are most 

 perennial herbs, their stems dying down to or beneath the sur- 

 face of the ground, where the persistent base is charged with 

 vigorous buds, well protected by the ground, for the next year's 

 vegetation. 



88. Man)' of the details and applications of ramification, of 

 most importance in morphology and descriptive botany, relate 



