FIRST LESSONS IN FRUIT GROWING— III. 



-N our last lesson, we studied the struct- 

 ure of the stem or trunk of a tree as it 

 appears in a cross-section of any of our 

 ^^ ordinary trees and we saw that it was 

 made np of an outer or dead bark and an in- 

 ner or live bark, of an outer or softer sap- 

 wood and an inner hard and dry heart-wood 

 in the centre of which might be seen the re- 

 mains of a soft spongy pith. 



Just here it may be well for us to study the 

 process of growth and learn how the trunk 

 increases in size. * 



How Tree Trunks Increase in Diameter. 



When a seed germinates, it sends down a 

 radicle, or little root into the soil, and sends 

 up a tiny shoot which bears leaves. As soon 

 as root, stem, and leaves are formed, the tree 

 has all of the parts necessary for growth. 

 Growth takes place in two directions, -that 

 is in length and breadth. 



First let us see how the trunk, or in fact 

 any of the parts, increases in thickness. 



The root-hairs and rootlets absorb from 

 the soil water, containing the plant-food in 

 solution. This water, usually spoken of as 

 the sap, passes from cell to cell through the 

 roots and sapwood of the stem and branches 

 to the leaves. In the leaves, it is spread out 

 over a wide surface exposing it to the action 

 of sunlight, where it undergoes considerable 

 change ; much of the water is given off 

 through the pores (Stoma) of the leaves, so 

 that the sap is reduced in bulk and thickened, 

 something as it is by boiling in sugar mak- 

 ing. 



Carbonic acid gas in also taken in by the 

 leaves from the atmosphere, and certain 

 chemical changes take place in the sap by 

 which its sugar is converted into starchy 



matter, and prepared to enter into the for- 

 mation of new growth. 



This elaborated material then passes from 

 the leaves down the branches and trunk and 

 roots just beneath the inner bark, forming a 

 sticky, half-liquid coating, over all the parts 

 of the trees, known as the cambium layer. 

 In the process of drying and hardening, this 

 forms a new layer of sapwood on its inner 

 side and a thin layer of new bark on its out- 



FiG. 2242. Scheme showing upward course of 

 water or sap, and d(wnward course of com'>ined 

 or elaborated plant food. (From U. S. bulletin, 

 Forestry for Farmers.) 



