FORESTRY AND CONSERVATION 333 



account of the great variations in those conditions. Thus the box 

 elder, an excellent shader in certain portions of the West, is a failure 

 as soil cover in others where it nevertheless will grow. 



We see, then, that in determining the shading value as well as 

 the shade endurance of one species in comparison with another, 

 with reference to forestry purposes, not only soil and climate but 

 also the character of foliage and its length of season must be 

 considered. 



Physiology of Tree Growth. As we have seen, root and 

 foliage are the main life organs of the tree. The trunk and 

 branch serve to carry the crown upward and expose it to the light, 

 which is necessary in order to prepare the food and increase the 

 volume of the tree, and also as conductors of food materials up and 

 down between root and foliage. A large part of the roots, too, aside 

 from giving stability to the tree, serve only as conductors of water 

 and food material; only the youngest parts, the fibrous roots, beset 

 with innumerable fine hairs, serve to take up the water and min- 

 erals from the soil. These fine roots, root hairs, and young parts 

 are therefore the essential portion of the root system. A tree may 

 have a fine, vigorous-looking root system, yet if the young parts and 

 fibrous roots are cut off or allowed to dry out, which they readily 

 do some kinds more so than others thereby losing their power 

 to take up water, such a tree is apt to die. Under very favorable 

 moisture and temperature conditions, however, the old roots may 

 throw out new sprouts and replace the fibrous roots. Some species, 

 like the willows, poplars, locusts, and others, are especially capable of 

 doing so. All trees that "transplant easily" probably possess this 

 capacity of renewing the "fibrous roots readily, or else are less sub- 

 ject to drying out. But it may be stated as a probable fact that most 

 transplanted trees which die soon after the planting do so because 

 the fibrous roots have been curtailed too much in taking up, or else 

 have been allowed to dry out on the way from the nursery or forest 

 to the place of planting; they were really dead before being set. 

 Conifers pines, spruces, etc. are especially sensitive ; maples, oaks, 

 catalpas, and apples will, in this respect, stand a good deal of abuse. 

 Hence, in transplanting, the first and foremost care of the forest 

 grower, besides taking the sapling up with least injury, is the proper 

 protection of its root fibers against drying out. 



The water, with the minerals in solution, is taken up by the 

 roots when the soil is warm enough, but to enable the roots to act 

 they must be closely packed with the soil. It is conveyed mostly 

 through the outer, which are the younger, layers of the wood of 

 root, trunk, and branches to the leaves. Here, as we have seen, 

 under the influence of light and heat it is in large part transpired 

 and in part combined with the carbon into organic compounds, 

 sugar, etc., which serve as food materials. These travel from the 

 leaf into the branchlet, and down through the outer layers of the 

 trunk to the very tips of the root, forming new wood all the way, 

 new buds, which lengthen into shoots, leaves, and flowers, and also 

 new rootlets, To live and grow, therefore, the roots need the food 



