102 



THE STEM. 



which lateral branches proceed ; as in most Fir-trees. Such a 

 trunk is said to be excurrent. In other cases the main stem is ar- 

 rested, sooner or later, either by flowering, by the failure of the 

 terminal bud, or the more vigorous development of some of the 

 lateral buds., and thus the trunk is lost in the branches, or is deli- 

 quescent, as in most of our deciduous-leaved trees. The first nat- 

 urally gives rise to conical 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 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 the knots in the centre of the trunk are the bases of branch- 

 es, 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. 



156. Definite and Indefinite Annual Growth of Branches, In the lar- 

 ger 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 (144), or else is early formed; and the de- 

 velopment is completed long before the end of summer, and 

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

 Fig. 127, Magnolia, Fig. 130, &c.), or with the uppermost axillary, 

 as in the Lilac (Fig. 129). Such -definite shoots do not die down 

 at all the following winter, but grow on directly, the next spring, 

 from the terminal or some of the upper axillary buds, which are 

 generally more vigorous than those lower down. In others, on 

 the contrary, the branches grow onward indefinitely through the 

 whole summer, or until arrested by the cold of autumn : they ma- 

 ture no terminal or upper axillary buds ; or at least the lower and 

 older axillary buds are more vigorous, and alone develope 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 Su- 

 mac and Honey Locust, are good illustrations of this sort ; which, 

 however, runs into the other mode through various gradations. 

 Perennial herbs grow after the latter mode, their stems dying 

 down to or beneath the surface of the ground, where the persistent 

 base is charged with vigorous buds, well protected by the ground, 

 for the next year's vegetation. 



