Leading Principles of the Growth of Trees. 1 3 



THE STEM AND BRANCHES. 



As roots are annual, biennial, or perennial, as they continue liv- 

 ing one, two, or more seasons ; so the stem is herbaceous or woody, 

 as it grows only one year or more in the latter instance hardening 

 into wood. Woody plants, when small, are called shrubs, as the 

 rose, gooseberry, and currant. When large, they are trees, as the 

 apple, pine, and oak. A dwarf apple, made small by budding any 

 common variety on the small Paradise stock, becomes a shrub. 

 Suckers are branches springing up from underground stems ; some- 

 times they come from mutilated roots. Runners are creeping stems, 

 which strike roots at the tips and form leaves there, as in the straw- 

 berry. A single strawberry plant will in this way produce a hundred 

 new ones or more in a summer ; and by care ten thousand by the end 

 of the second year, a million the third, and so on. 



Outside-growing woody stems (or those which are two-cotyle- 

 doned) are made up of the bark, wood, and pith. The liber, or inner 

 bark, lies next the wood ; and the rind or outer bark, on some trees, 

 forms gradually into a thick, hard, corky substance, termed cortical 

 layers. When young it is the green bark, and performs an office in 

 the growing plant similar to that of the leaves. The sap descends 

 from the leaves through the inner bark, and deposits new layers of 

 both wood and bark yearly. Thus the newest bark is inside, and 

 the newest wood outside. 



Wood. The outer wood, which is the youngest and freshest, is 

 called the alburnum or sap-wood. The heart-wood is the older, 

 harder, and usually more dried portion ; and it bears the same rela- 

 tion to the sap-wood, as the cortical layers do to the liber. The 

 pith, in young plants, performs a useful office by retaining moisture ; 

 but in old trees it becomes dry, shrivelled, and useless, and trees 

 grow as well where it has been cut out. 



Branches. These consist of main branches, or limbs ; secondary 

 or smaller branches ; and shoots, or the extremities, being one year's 

 growth. Thorns are a modification of branches, and are sometimes 

 simple, as in the common thorn ; or branched, as in the honey- 

 locust Ungrafted pear-trees often present all the intermediate forms 

 between perfect branches and perfect thorns. Prickles grow only 

 from the bark, and when the bark is stripped off they are all taken 

 off with it ; but thorns remain attached to the wood. 



Buds are of two kinds, leaf and flower. The former grow into 

 branches, the latter produce fruit. To distinguish these buds is of 

 great importance to the cultivator of fruit-trees. In Fig. 3, A repre- 



