Georgia State College of Agriculture. 



and with the character of soil. Certain trees, as hickory, walnut 

 and white pine, develop a stout tap root which extends perpendic- 

 ularly into the soil. With others, as maple, red gum and cotton- 

 wood, the roots tend to spread laterally in the upper layers of soil, 

 producing a shallow root system. With others again, as beech, red 

 oak and chestnut, several strong roots penetrate obliquely into the 

 soil. A few trees will adapt themselves to soil conditions, in a 

 shallow soil developing surface roots, and in a deep soil developing 

 deep lateral roots. A shallow soil may be due to hard-pan, bed 

 rock or soil water. In the latter case it is susceptible of improve- 

 ment through drainage. In general it may be said, however, that 

 unless the soil is deep enough for a tree to develop its characteristic 

 form of root system, the growth of the tree will be slow and the 

 form irregular and stunted. The characteristic form of the root 

 system of many trees may be studied on those upturned by the wind. 



The Stem. The stem or trunk (occasionally termed "bole"), sup- 

 ports and elevates the crown. It conveys the soil moisture (sap) 

 from the roots where it has been absorbed, to the crown where it 

 is used. The stem also serves as a storehouse for surplus food 

 material. From an economic standpoint, the stem is the most 

 valuable portion of the tree. Upon its size and shape depends the 

 amount of lumber, cordwood, ties, or other product that may be 

 obtained. Each species has its characteristic form of stem, some 

 trees producing a long cylindrical bole free of branches, others 

 developing a short tapering bole more or less branched and crooked. 

 Often the same species develops two very different forms, depending 

 upon whether it is growing in the open field or in the forest. One 

 may be short with a long crown and rapidly tapering stem, the 

 other tall and straight with a short crown and a cylindrical stem. 



The bark is characteristic of the species and varies in thickness, 

 color, roughness and markings. It serves as protection against heat, 

 cold, mechanical injury and the entrance of disease (rot). Occa- 

 sionally it forms a valuable commercial product, as in the case, of 

 hemlock (spruce) and chestnut bark in the production of tannic acid. 



Crown. The crown is composed of branches, twigs and leaves, 

 together with buds, flowers, fruit, etc. As it has to do with many 

 vital processes it is the most important part in the life of the tree. 

 As a result of almost endless division the branches enable the tree 

 to present the greatest possible extent of leaf surface to the action 

 of the sunlight and air. Unlike the roots the branches have a more 

 or less definite arrangement. 



The leaves of the tree function in much the same way as do the 

 lungs and stomach of an animal. In them are carried on the pro- 

 cesses of respiration (breathing the breaking down of tissue 

 through oxidation), transpiration (the loss of surplus moisture 

 through evaporation), and photosynthesis (the combination of car- 

 bon dioxide from the air with the mineral matter of the sap to form 

 sugar). Protosynthesis is carried on by the green matter of the 

 leaf (chlorophyl) under the influence of sunlight. In darkness 

 (often in subdued light) this process is interrupted. 



