PLANTING. 5 



The presence of leaves is essential to the growth of buds and branches, 

 and consequently to that of the pith in these and in the roots; but the 

 leaves are not otherwise necessary to the formation and growth of the 

 fibres or radicles of the root, as these are produced in abundance when the 

 plant or tree is leafless, and even during winter when the ground is covered 

 with frost and snow, the reservoir of nourishment in the pith being 

 probably sufficient for that purpose. 



From these facts and others which might be brought forward, it is clear 

 that the uses of the pith in the formation of buds in the branches of the 

 tree, and of fibres or radicles in the root, and in the support of these 

 during the first stages of growth, are analogous to the important functions 

 of the seed leaves in the first stages of growth of the seedling plant. The 

 pith of a radicle or fibre may readily be traced into that of the root, and 

 the same is precisely the case in a branch with relation to the stern of the 

 tree. The respective uses of these organs are only for the first and early 

 stages of growth ; and, after that, they may be lost without any apparent 

 injury to the further progress of the parts in question : the cotyledons dry 

 up and fall away as the healthy progress of the roots and leaves advances, 

 and the pith disappears, or its identity is lost in the wood, as that part of 

 the structure which surrounds it approximates to maturity. * 



The wood stands next in order to the pith, it is formed of indurated 

 vegetable fibre, and occupies the space between the pith and the bark; it 

 constitutes the bulk and strength of the subject. The yearly growth or 

 increase of the wood is defined by circular lines or concentric layers clear 

 to common observation in a transverse section of any root, branch, or 

 stem. The discriminating characters of the wood being more obvious in 

 the stem, than in the root or rootlets, we shall consider it more particularly 

 when mentioning the stem. 



The baric covers the wood in every part of the tree, and is the most 

 important organ of vegetable life, for the pith may be lessened, the wood 

 may be partially or even wholly taken away, and, the leaves may be 

 stripped off, and yet the tree may recover, but when deprived of its 

 bark, the root, stem, or branch of a tree dies. It is therefore of the 

 greatest importance to the practical planter, that the bark of the roots and 

 of the exposed system of his plants should be preserved free from the 

 slightest injury. 



The bark when divided horizontally shews three distinct parts, the liber, 

 or inner bark, which lies next to the wood ; the cellular tissue, or paren- 

 chyma, which is distinguished in the bark of the exposed system of the 

 plant by its fine green colour, but which is colourless in the bark of the 

 root ; and, lastly, the epidermis, or outer bark, which is the universal 

 covering of every part of a tree. 



* A scion grafted on a stock, and a bud separated from its parent shoot and inserted 

 into the bark of another tree, may at first sight offer proofs going to invalidate the opinion 

 of the important uses of the pith in the formation of buds and fibres ; but before the scion 

 and the bud are taken off; or are in a fit state for the purposes of budding and grafting, the 

 pith of the parent stock has already performed its offices. The important experiments of 

 Mr. Knight on this subject prove that the pith may be removed in part without effecting 

 the general health of the tree, just as the cotyledons may be removed from the young 

 plant after having established its root and stem, with a continuation of pith to originate 

 new buds, or embryo branches and radicles. We often meet with roots, which from severe 

 injuries by mutilation at an advanced age of the tree, or by the injurious effects of a 

 damp ungenial soil at an earlier period of growth, have lost the entire substance of the 

 pith and wood, and present the appearance of a hollow tube, have yet young fibres or 

 radicles issuing from their sides and continued as in roots where the pith and wood is 

 perfect ; on examination, however, these young fibres may be traced through the bark into 

 the hollow of the root, demonstrating the origin of the radicle from the pith. 



