234 ANNUAL. REPORT OF THE Off. Doc. 



cells between bark and wood the living mater in the cells is in con- 

 tinuous connection throughout the growing tissues. Later on, as 

 the cell walls thicken, each lives to itself and carries on the making 

 of the wood until all the living matter is used up and the wood is 

 finished, and we call it "heart" wood, really dead wood, for the heart 

 of a tree merely remains to hold the tree in position, while the life 

 goes circling on around it. The heart may decay and the tree get 

 hollow, but it will keep on growing, but if you cut through the grow- 

 ing cells all arouud the outside of the tree it will be killed. 



The leaves as well as other parts of the tree are made up of these 

 cells, but in these the living matter contains certain green granules 

 which can easily be seen under the microscope, and which from their 

 abundance give the naked eye the characteristic color of the leaf. 

 In every leaf, and especially on the under side of the leaf, there 

 are numerous minute openings which require a microscope for their 

 detection. On each side of these openings there is a cell shaped 

 like our lips, which give the openings the appearance of mouths 

 under the microscope, and they are really the mouths through which 

 the plant gets food from the air. In some leaves there are 70,000 of 

 these minute pores to the square inch. They open into the interior 

 of the leaf where the cells containing the green matter are loosely 

 arranged. During the hours of sunshine, and at no other time, 

 these mouths are open, and they close in sunshine when a plant 

 wilts from lack of moisture so as to check evaporation and give the 

 plant a chance to recover. In the air there is always a small per- 

 centage of carbon dioxide or carbonic acid as it is commonly called, 

 which when in excess is poisonous to animal life. When the sun 

 shines the mouths in the leaf open and the air with the carbon di- 

 oxide enters the leaf and comes in contact with the green granules. 

 This green matter has the wonderful power to break up the com- 

 bination of carbon and oxygen throwing back the oxygen to purify 

 the. air and taking the carbon for the use of the plant. Then in the 

 leaf laboratory the food brought up from the soil in the soil water 

 taken in by the roots is combined with this carbon and the living 

 matter uses it for the work of what we call growth. The nitrogen, 

 coming from the soil, continually renews the vigor of the living mat- 

 ter, while the materials from the air, which scientists call carbo- 

 hydrates, because they are composed of carbon, hydrogen and oxy- 

 gen, are used by the living matter to construct new cell walls and 

 woody material. While the great bulk of the plant structure thus 

 comes from the air. the matters that the roots take from the soil 

 are nevertheless of vital importance. Let us study the root and 

 see how the plant gets these materials from the soil. Place several 

 layers of thick blotting paper in a saucer and wet them. Then on 

 the wet paper lay some seeds of ordinary string beans. Cover the 

 saucer with a pan of glass and set in a warm place. They will soon 

 sprout and throw out roots over the wet paper. By examining these 

 carefully you will see that the extreme tip is pointed and naked, 

 making what is called the root cap. New cells of growth form back 

 of this root cap and push it forward through the soil, and renew- 

 ins: it as it vrears awav on the outside from behind. Just back of 

 this root cap you will see that a portion of the root is covered with 

 a velvety coating of minute hairs. These root hairs are the only 

 part of the root engaged in taking in foo4 from the eoil, and from 



