Leading Principles of the Growtli of Trees. 1 5 



Buds are lateral, when on the side of a shoot ; and terminal, 

 when on the end. Terminal buds are nearly always leaf buds, and 

 usually being larger and stronger than others, make stronger shoots. 

 All buds are originally formed as leaf buds, but the more feeble are 

 generally changed to fruit buds. Now, it happens that on many 

 kinds of trees, the feebler buds are on the lower parts of shoots (by 

 lower is meant furthest from the tip), and these consequently often 

 change to fruit-buds. This change in some kinds of trees, as cherry 

 and plum, takes place the year after they are formed ; and in others 

 the same year, as, for instance, in the peach and apricot. This 

 transformation is a very curious process, and is effected by the em- 

 bryo leaves changing to the organs of the flowers. A contrary 

 change of stamens to flower leaves produces double flowers. 



Latent Buds. Only a small proportion of all the buds formed 

 grow the second year ; the rest remain dormant or latent for years, 

 and are made to grow and produce shoots only when the others are 

 destroyed. 



Adventitious Buds are produced by some trees irregularly any- 

 where on the surface of the wood, especially where it has been 

 mutilated or injured ; and they form on the roots of some trees 

 which are cut or wounded. In these cases such trees may be 

 usually propagated by cuttings of the roots. 



Leaves. These are commonly made up of two principal parts, viz. 

 the framework, consisting of the leaf-stalk, ribs, and veins, for 

 strengthening the leaf, and supplying it with sap ; and the green 

 pulp, which fills the meshes or interstices. The whole is covered 

 with a thin skin or epidermis. The green pulp consists of cells of 

 various forms, with many air-spaces be- 

 tween. The cells are commonly placed 

 very compactly together on the upper 

 side of the leaf, and more loosely, or with 

 air-spaces, on the lower side hence the 

 reason that leaves are usually lighter- 

 colored below. Fig. 4 is a highly mag- 

 nified section of a leaf, showing the green 

 cells, air spaces, and epidermis above 

 and below. Leaves have also breathing 

 pores, through which moisture and air 

 are absorbed, and vapor given off. Fig- 4- 



They are so small as to require a good M a S nified cross section of leaf. 

 microscope to discover them ; and they vary in different plants 

 from 1,000 to 170,000 on a square inch of surface. The apple and 



