PLANTING. 9 



young, the bark in question is gradually converted into root-bark ; during 

 this conversion of the stem-bark to that of the root, the plant advances 

 but little, if any, in growth, but exhibits an unhealthy appearance by the 

 paleness of its leaves, and the weak growth of shoots. The same effects 

 are in a great degree observable from the opposite error, of planting too 

 shallow, which is when a portion of the root nearest to the stem is left 

 above the ground. This exposed portion of the root-bark in time gains 

 the green colour in its parenchyma ; and although no portion of it is 

 ever found to decay, as in the former instance, yet, for a time, the plant 

 makes but little progress in the growth of wood : if a fruit tree, the effect 

 appears to be to increase the formation of fruit buds, and to stimulate the 

 functions of the tree to bear fruit. It may not be devoid of interest to re- 

 mark here, that this is a more efficacious mode of inducing a free grow- 

 ing though barren fruit-tree to bear fruit, than any of those recommended 

 for that purpose, such as ringing, or placing an iron ring round a branch 

 to prevent the annual increase of bark on the space occupied by the ring, 

 cutting the bark in the mariner of a circular incision of a branch, dividing 

 the roots, and by reversing the natural direction of the branches. It may 

 be unnecessary to add, that the above facts point out the importance of 

 planting every tree not deeper in the ground, nor farther out of the surface, 

 than the root occupied in the soil previous to transplantation ; most essen- 

 tially when the produce of wood or of timber is the primary object desired. 



The stejn, trunk, or bole, constitutes the principal body of a forest-tree. 

 It is the medium of communication between the root and the branches, 

 leaves, flowers, and fruit or seed. By the exercise of this function it ob- 

 tains its yearly increase of substance, marked by the white circular lines 

 apparent on the surface of a transverse section of the stem of every species 

 of forest-tree. By counting the number of these circles the age of the tree 

 may with certainty be determined. 



It was before observed that the structure of the root was similar to that 

 of the organization of the stem and branches; but a more particular 

 notice of the constitution of the wood was referred to this place. 



A close examination * of a horizontal section of the wood of a trunk or 

 branch of a tree, will exhibit two very distinct appearances. 



1st. A series of white and shining laminse, which radiate from the pith 

 to the bark (jig. b, ])f. These generally straight, or sometimes interrupted, 

 lines are termed the silver grain or medullary rays of the wood. These 

 vary as to size and arrangement, termed primary or secondary rays, con- 

 tinued in one straight line from the pith to the bark, or interrupted and 

 broken in the course of their direction, according to the species of tree 

 which affords the wood in question. They appear to be composed of 

 cellular tissue, and to originate from the pith, or, in a word, are a linear 

 lateral extension of that organ. These medullary rays are elastic and con- 

 tractile, as is evident to every one who has observed the effects of the 

 extremes of dry and of moist weather on the section of a felled tree. 



2d. A series of concentric layers, or circles, termed the spurious grain. 

 These consist of tubular vessels of smaller or larger diameters, arranged 

 in lines or groups varying according to the genus and species of the tree 

 to which the wood belongs. 



* With a common or four-power microscope. A thin slice of the substance is, perhaps, 

 the most convenient for examining. When placed under a high magnifying power the 

 be auty, order, and arrangement of the tubular and cellular texture will reward the observer. 



f These should be examined with a magnifying glass, for the texture of the different 

 woods exhibited will thereby be more satisfactorily compared with, the descriptions 

 which accompany them. 



