A Tree is a Living Thing 



poses, from fattening hogs to produc- 

 tion of industrial alcohol. Most of the 

 cellulose used at present, however, is 

 converted into pulp and paper. 



The rest of the wood consists mostly 

 of Hgnin, which is a binding material 

 composed, like the cellulose, of carbon, 

 oxygen, and hydrogen, but of an en- 

 tirely different and more complicated 

 chemical structure than cellulose. Lig- 

 nin is not so useful as cellulose at pres- 

 ent, but there is little doubt that valu- 

 able products will be made from it. 



Besides cellulose and Hgnin, wood 

 contains a small quantity of different 

 substances starch, fats, sugar, resins, 

 tannins, and many others and is liter- 

 ally saturated with water. 



About 10 percent of the wood mass 

 of a tree is found underground in the 

 form of roots. The root system of a 

 large tree is enormous. The total length 

 of all roots of a big spreading oak tree 

 amounts to many hundreds of miles. 

 The function of the root is to provide 

 water and minerals for the tree and 

 to anchor it securely to the ground. It 

 is important to keep in mind that the 

 roots are part of a living organism and 

 that they need air, food, and water 

 for growing. Mistreatment of roots, 

 such as tramping the soil above them, 

 flooding them for long periods of time, 

 or burying them too deeply, will af- 

 fect the welfare of the whole tree. 



THE TREE COMES OF AGE. Our tree 

 gradually becomes taller and broader, 

 and in the course of time it reaches ma- 

 turity. The complicated mechanism 

 functions with the precision of a ma- 

 chine, and its many vital processes are 

 well coordinated. Some of the proc- 

 esses, such as respiration or digestion 

 of fats, are strikingly similar in both 

 plants and animals. Others, as mineral 

 nutrition, are found only in the plants. 



LET us CONSIDER first the process 

 of photosynthesis that is, the build- 

 ing with the energy of light. In this 

 process, organic matter is formed liter- 

 ally from thin air and water. The air 

 contains minute amounts of carbon di- 



oxide (0.03 percent by volume or three 

 parts in 10,000 parts of air) . Through 

 millions of small pores, or stomata, on 

 the leaf surfaces, air penetrates the 

 leaves and gives up about 10 percent 

 of its meager supply of precious car- 

 bon dioxide to the tree. In the leaf 

 cells are found small particles called 

 chloroplasts; these contain a green sub- 

 stance, chlorophyll, similar in structure 

 to the hemoglobin of the blood. In 

 fact, in reflected light chlorophyll ap- 

 pears not green but blood red. 



Carbon dioxide unites with the 

 chlorophyll and in a chain of reactions, 

 regulated by the enzymes, it combines 

 with oxygen and hydrogen of water to 

 form sugar. An excess of oxygen is re- 

 leased in this process. The energy that 

 is needed for transformation of carbon 

 dioxide and water into the organic 

 substance (sugar) is supplied by sun- 

 light. Only about 1 percent of the solar 

 energy that falls on a leaf is used for 

 photosynthesis. The sugar formed in 

 the process of photosynthesis is dex- 

 trose. From it 95 percent of the body 

 of the tree is ultimately made by a 

 series of complicated reactions. Dex- 

 trose may be converted into other 

 sugars or it may be combined with 

 nitrogen to form the amino acids, the 

 building blocks from which proteins 

 are made and on which all life, both 

 plant and animal, depends. Part of the 

 dextrose is also used for other purposes, 

 such as conversion into starch, fats, and 

 other substances. 



The most favorable conditions for 

 photosynthesis are mild temperatures 

 (about 70 F.) and diffused, moderate 

 light. On hot, bright, summer days the 

 efficiency of photosynthesis goes down. 

 An ample supply of water is essential. 

 When the soil is dry and not enough 

 water is delivered to the crown, the 

 rate of photosynthesis declines. Fer- 

 tility of the soil is also important, for 

 the building of the tree body requires 

 an ample supply of mineral elements. 



Respiration is another life process. 

 Like other living organisms, a tree must 

 respire. The process of respiration 

 consists of oxidizing (burning at low 



