165) 
Erect growth will result, with very few lateral branches, thus forming 
from the first the clean, straight trunk so necessary to high quality in 
timber. 
The Catalpa, though not a shade-enduring tree, retains its lateral 
branches with such persistence as to require dense-shading nurses to 
assist it in shedding them. The Scotch Pine, when grown in full sun- 
shine and with plenty of room, as in parks or lawns, seldom forms a 
straight trunk, but usually divides into heavy branches near the 
ground, thus making its timber of little value. Close-shading neigh- 
bors will correct this fault and result in a straight stem, from which 
the lower laterals soon fall. Care must be exercised with all the heavy- 
branched conifers, such as the Scotch, Austrian, Rock (Bull), and 
Red Pines, not to overtop them with shading trees. Tliey are benefited 
by side shade, and even that must be reduced as the trees advance; 
but they are intolerant of shade overhead. The White Pine will endure 
more shade during youth than the heavier branched Pines named, but 
it also requires unobstructed light at the top after, say, seven to ten 
years, and needs full sunshine as it approaches maturity. 
Indeed, as was said at the beginning of this chapter, all trees are 
benefited by full light, viewed from the standpoint of growth. When 
the use to be made of their timber is considered, however, it may be 
added that all trees will profit by the formative influence of close plant- 
ing with shading neighbors that will prevent the light from reaching 
the lower branches as the trees develop. In the absence of light the 
foliage is unable to do its work, the branches die from Jack of nourish- 
ment, and within a few years fall away. The upper part of the crown, 
meanwhile, is elongated in an effort to reach full light, and thus the stem 
grows straight and tall, and all the wood laid on the trunk is free from 
knots. After the stem is well formed additional light should be given 
the best trees by thinning out the inferior species or specimens, and 
thereafter increased volume growth will result. 
Relative height growth.—In determining rules for mixed planting, the 
effect of light upon tree growth is intimately associated with the 
relative height growth of various species. 
Not only has each species an average height in maturity, enabling 
us to make a classification on this basis (White Pine, Tulip, and White 
Oak being high trees as compared with Boxelder and Mulberry, or 
Wild Plum and Scarlet Haw), but the growth in height ismuch greater 
at one period than at another. Generally speaking, all species make 
their principal height growth during the earlier part of their lives, the 
increase in volume of usable material being greater thereafter. But 
during this time of rapid height growth there is much diversity in the 
action of species. The White Spruce is very slow in growth during 
the first years, and its growth thereafter, though much more rapid, 
never equals that of Scotch and White Pine. The Colorado Blue Spruce 
is much slower than White Spruce at all stages of its development. As 
