TREE PHYSIOLOGY 41 



times it carries the shrinking cotyledons with it, 

 where under the influence of air and light they turn 

 green and perform the functions of leaves until 

 more permanent ones can be formed. 



The seedling is now well started. Growth goes 

 on rapidly. Branches are thrown off and buds 

 and leaves formed. If we cut the stem of a young 

 seedling across, it seems to be composed of a loosely 

 packed pith and an epidermis. Examined more 

 closely, the outer portion of the pith is seen to be 

 more solid in texture. It is the beginning of the 

 future wood. Between the outer and inner piths 

 lies a bundle of longitudinal strands, the future 

 cambium layer. 



By the end of the first year the young tree has 

 taken on its permanent form on a small scale. In 

 structure it is composed of the main stem, branches, 

 shoots, leaves and buds. The points of growth 

 are at the tips of each branch or shoot. The tree 

 also grows in girth throughout its body exogenically 

 or by development outward. The branches group 

 themselves in definite arrangements. The points 

 where leaves appear are called nodes. The stem- 

 spaces between the nodes are internodes. Some of 

 the branches are observed to be rudimentary and 

 destined never to develop. This is due to the ever- 

 present tendency of the sap to mount as high as 



