28 GENERAL PRINCIPLES. 



organize new layers of woody fibre, that descend and cover 

 those of the previous year, and thus g-rowth proceeds from 

 year to year. Between each year's growth tliere is gener- 

 ally a line, in some cases more conspicuous than in others, 

 that marks off the formation of each year, so that we are 

 able to reckon the ages of trees with great accuracy by 

 these rings. When it happens that a tree, from certain 

 circumstances, makes more growth one season than an- 

 other, we find the ring of that season larger. The new 

 wood in all our northern trees is always formed between 

 the inner bark and the last layer of wood, so that one 

 layer is laid upon, and outside of another, and the bark 

 is continually pressed outwards. 



The new layers of bark are also formed at the same 

 place, or wUhin the previous one. From this mode of 

 growth, it results that each layer of wood is more deeply 

 imbedded as others are formed above it ; and eacli layer 

 of bark is pressed outwards as others are formed within 

 it. In some cases, as in the cherry, for example, the bark 

 is so tough as not always to yield to the general expansion 

 of the tree, and slitting is resorted to for the purpose of 

 preventing an unnatural rupture, which would e\'entually 

 take place by the continued pressure of growth from 

 within. 



Section 3. — Branches. 



branches are the divisions of the stem, and have an 

 organization precisely similar : they are designated as, 



1st. Main Uranches (F, fig. 1) ; those thnt are dii-ectly 

 connected with the stem or trunk. In pyramidal trees, 

 they are called lateral branches. The branches of different 

 species and varieties of fruit trees, differ much in their 

 habits of growth ; and it is highly important to the 

 planter to consider these peculiarities, because certain 

 habits of growth are better adapted to particular circura- 



