HOW TREES GROW. 



271 



FIG. 30. Dormant bud K, on a 12-year-old branch 

 of beech. Tin 1 bml is still capable of development 

 and ia connected with the pith, mm, of the stein by 

 a fine tram of pith, >S'. 



some of the buds, giving thereby better chance to the remaining ones. This priming of buds is, 



where practicable, often better practice than the pruning of limbs. 



Since the tree does not grow in length except by its buds, it is evident that a limb which 



started to grow at the height of (i feet has its base always (i feet from the ground, and if allowed 



to grow to size, must be surrounded by the wood which accumulates on the main stem or trunk. 



If a limb is killed and broken oft' early, only a slender stub 



composed entirely of rapidly decaying sapwood is left, 



occasioning, therefore, only a small defect in the heart of 



the tree; but if left to grow to considerable age, the base 



of the limb is incased by the wood of the stem, which, 



when the tree is cut into lumber, appears as a knot. The 



longer the litiib has been allowed to grow the farther out is 



the timber knotty and the thicker is the knot. If the limb 



remained alive, the knot is "sound," closely grown together 



with the fibers of the tree. If the limb died off, the remain- 

 ing stub may behave in 

 different ways. In pines 

 it will be largely com- 

 posed of heart-wood, very 

 resinous and durable; 

 separated from the fibers 

 of the overgrowing wood, 

 it forms a "loose" knot, 

 which is apt to fall out of 

 aboard, leaving a hole. 



In broad-leaved trees, where no resin assists in the process of 

 healing, the stub is apt to decay, and this decay, caused by the 

 growth of fungi, is apt to penetrate into the tree (fig. 3li). In 

 parks and orchards pruning is resorted to, and the cuts are 

 painted or tarred to avoid the decay. In well-managed forests 

 and dense woods in general the light is cut off, the limb is killed 

 when young and breaks 

 away, the shaft "clears it- 

 self," and the sound trunk 

 furnishes a good grade of 

 material. The difference 

 in development of the 

 branch system, whether 

 in full enjoyment of light, 

 in open stand, or with the 

 side light cut off, in dense 



position, is shown in the accompanying illustration (fig. 33). 

 Both trees start alike; the one retains its branches, the 



other loses them gradually, the stubs being in time over- 

 grown ; finally, the second has a clear shaft, with a crown 



concentrated at the top. while the first is beset with 



branches and branch stubs for its whole length (fig. 34). 

 When ripped open lengthwise, the interior exhibits 



the condition shown in fig. 30, the dead parts of the knot 



being indicated in heavier shading. Since the branches 



grow in more or less regular whorls, several knots, stumps, or limbs are met every to L'4 inches 



through the entire stem. 



Hence, in forest planting, trees are placed and kept for some time close together, in order to 



decrease the branching in the lower part of the tree and thus produce a clean bole and clear lumber. 



FIG. 31. Section through a 12-year-old stem 

 of beech, showing manner of bud and limb 

 formation, a, dormant buds; &, their trace 

 of pith extending to the pith of the stem; 

 c, a limb which started two years ago from 

 a dormant bud; d, normal limb; , a limb 

 dead for four years; /, adventitious buda. 



Fio. 32. Section through a partly decayed knot in 

 oak wood, a, wood of tho knot ; b ;uid e, wood c;il- 

 lusol'tliOMtfin covcrini; llic wound ; shaded portion. 

 decayed wood; black part, a -javity remaining. 



