r 2 Leading Principles of the Growth of Trees. 



The cells of plants usually vary from i-3ooth to i-5ooth of an inch 

 in diameter, and it is obvious that during vigorous growth the plant 

 must form them with great rapidity. A shoot of asparagus increases 

 the length of one cell every ten seconds ; and as its diameter embraces 

 many thousands, from fifty to a hundred million are formed every 

 day. The building up of the plant of these cells has been compared 

 to the erection of a house by the successive addition of bricks ; but 

 if as many bricks were daily added to a structure, they would be 

 enough to make a building daily larger than the great pyramid of 

 Egypt, or the Coliseum at Rome. Yet every one of these cells is 

 as perfect and finished as the finest work of art. 



THE ROOT. 



The root consists of several parts. The main root, called also 

 the tap root, is the large central portion, extending downwards. 

 In many plants or trees, however, it is divided as growth advances, 

 until lost in laterals or side branches. The fibres or rootlets are 

 the small thread-like roots proceeding from the laterals ; and lastly, 

 and smallest of all, the new fibres are furnished with root-hairs, 

 scarcely visible without a microscope. The whole surface of roots 

 continue to absorb moisture from the soil so long as they are fresh 

 and new ; and the newer portions, near the tips, absorb most freely. 

 Old roots, covered with a hard or horny bark, imbibe almost none. 

 The root-hairs convey moisture into the fibres with rapidity. 

 Young trees, when dug up for transplanting, have most of the fibres 

 and root-hairs torn from them, and they would suffer serious injury 

 or die, but for the power which they possess of rapidly reproducing 

 them under favorable influences. 



The collar is the point of union between the root and the stem, but 

 its place may be easily changed in many young plants by banking 

 up the stem, which will emit new roots above. Or, a branch may be 

 buried, as in layering grape-vines, honeysuckles, gooseberries, and 

 many other woody plants. Small portions of roots attached to a 

 graft will often produce a new plant ; this is especially the case with 

 the grape and rose, which are extensively propagated in this way ; 

 and also in some degree with the apple, of which, however, when 

 thus root-grafted, larger portions should be employed of the roots 

 of one-year, or at most two-year seedlings. 



