WINTER MEETING. 305 



branches, and to apply many other methods of treatment which bear 

 directly upon this subject. A thorough understanding of the move- 

 ment of sap is of great advantage, however. It is hoped that the fol- 

 lowing may contain some hints that may enable the cultivator to better 

 investigate this subject for himself and to better understand the why 

 and wherefore of it. 



For practical purposes let us consider the tree as consisting of 

 root, stem and leaves. The stem is composed of a central pith, out- 

 side of this the wood, between the bark and wood, is the growing 

 layer and outside this is the bark. These different parts are made up 

 of small hollow cells, some of them are nearly spherical, and others, 

 particularly those of the wood, are long and tube like. 



The crude sap is taken in through tiny root hairs, which are very 

 abundant and may sometimes be seen with the naked eye along the 

 growing tips of the tiny roots or rootlets. These root hairs are com- 

 paratively short lived. New ones are continually being formed near 

 the tip of the rootlet as it increases in length, and the older ones 

 farther back disappear. Being very delicate, they are also easily in- 

 jured. Since the plant relies mainly upon these root hairs for taking 

 up the sap from the soil, it is essential that in transplanting tender 

 seedlings, these root hairs should not be injured more than is neces- 

 sary. Many of them are broken and left in the soil in removing the 

 plant, and exposure to drying atmosphere very soon kills them. If a 

 root is broken off it can take in some moisture through the wound 

 just as a cut flower in a vase of water can take up moisture through the 

 cut end of the stem. Transplanted plants are liable to wilt for a time, 

 until new root hairs can form in sufficient numbets to take up the 

 requisite supply of moisture. 



The leaves bear much the same relation to the tree that the 

 stomach and lungs do to the animal. When the sap is taken up by the 

 roots it is carried to the leaves and there digested in the presence of 

 the green coloring matter. JSTone of the crude sap can in any way pro- 

 mote growth until it has thus been acted upon in the leaves. It is 

 essential to remember that it passes upward through the sap wood. 

 This may be shown by the fact that if a ring of bark is taken off around 

 the trunk, laying bare the wood, the leaves above this girdle will not 

 wilt, but will still be supplied with moisture. This is true in hollow 

 trees, in which the pith and heart would have rotted away. In the 

 leaves (and incidentally in some green-colored stems) the food materials 

 are digested, and most of the water of the sap is evaporated into the 

 air. The digested food i8 then distributed, in the growing layer, to all 

 H— 20 



