Structure and Growth of Wood. 



75 



removing the layers of growth that have formed since any given 

 period. ' 



2(54. A leaning tree has the center of growth on the upper side, 

 and the same is generally observed in branches near the place where 



64. Excentric Forms of Growth. 



they come out of the tree. This excentric growth is very common 

 in tropical woods, and in some species there are sec- 

 ondary centers of growth within the principal ones. 



265. In some of the conifers, especially in the firs 

 and spruces, there is a remarkable symmetry in the 

 branches, several (often five) springing from a single 

 point, and dividing the angular space equally between 

 them. The vertical distance between these branches 

 generally represents a year's growth in length, and a 

 cross-section above a set of branches has, of course, 

 one less number of rings than would be found below 

 them. 



266. The rate of growth in wood differs 

 greatly, according to the soil, elevation, aspect, cli-j 

 mate, humidity, temperature, prevailing winds, and 

 other causes. It has been estimated that, on a gen- 

 eral average, a forest will, if not specially cared for, 

 grow about a cord of wood on an acre per year. It 

 may often be much less than this, or much more, and 

 may be largely increased by clearing out the under- 

 growth, and thinning out the trees that crowd too 

 closely. It may be stimulated by fertilizers, applied 



as a top dressing, and may be retarded by taking spruce, 

 away the litter that accumulates from the fall of leaves. 



