2G8 FORESTRY INVESTIGATIONS U. S. DEPARTMENT OF AGRICULTURE. 



locust, ^hite ash, green ash, red pine, bull pine, sycamore, larch, black birch, inesquite, the 

 hickories. 



Light-demanding when mature, but enduring moderate shade in youth : The oaks, white pine, 

 black cherry, catalpa, silver maple, red maple, the elms, tulip, yellow biich. 



Shade-enduring: Beech, sugar maple, box elder, mulberry? hackberry, hemlock, red cedar, 

 Douglas spruce, white fir, white spruce, arbor vita*, and white cedar. 



PHYSIOLOGY OF TREE GROWTH. 



As we have seen, root and foliage are the main life organs of the tree. The trunk and 

 branches serve to carry the crown upward and expose it to the light, which is necessary in order 

 to piepare 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 minerals 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 oft or allowed to dry out, which they readily do — some kinds more so than others — 

 thereby losing their powers to take up water, such a tree is apt to die. Under very favorable 

 moisture and temperature conditions, however, the old roots may thiow 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 v probably possess this capacity 

 of renewing the fibrous roots readily, or else are less subject 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 weie 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 

 seedling 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 pait transpired 

 and in part combined with the carbon into organic compounds, sugar, etc., which serve as food 

 mateiials. These travel from the leaf into the bianchlet, and down through the outer lasers 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 elaborated in the leaves, just as the leaves need the water sent up from the roots. 



Hence the interdependence of root system and crown, which must be kept in proportion when 

 transplanting. At least, the root system must be sufficient to supply the needs of the crown. 



"SAP UP AND SAP DOWN." 



The growing tree, in all its parts, is more or less saturated with water, and as the leaves, 

 under the influence of sun and wind and atmospheric conditions generally transpire, new supplies 

 are taken in through the roots and conveyed to the crown. This movement takes place even in 

 winter, in a slight degree, to supply the loss of water by evaporation from the branches. In the 

 growing season it is so active as to become noticeable: hence the saying that the sap is "up," or 

 "rising," and when, toward the end of the season, the movement becomes less, the sap is said to 

 be "down.' 7 But this movement of water is always upward; hence the notion that there is a 

 stream upward at one season and in one part of the tree and a stream downward at another 

 season and perhaps in another part of the tree is erroneous. The downward movement is of food 

 materials, and the two movements of water upward and food downward take place simultaneously 

 and depend, in part at least, one upon the other, the food being carried to the young parts, 

 wherever required, by a process of diffusion fiom cell to cell known as "osmosis." 



