GROWTH OF THE STEM. 



33 



it to be tliirty-one feet in circumference. There 

 was another close by which I did not see, tliirty- 

 thrce feet, and I heard of one not less than forty 

 feet. The trunks are also very remarkable for 

 their smoothness, cylindrical figure, absence of 

 branches, and having very nearly the same girth, 

 with a length from sixty to ninety feet. The 

 crownof this tree, whereitisirregularly branched, 

 is small, and out of proportion to the trunk, 

 and the foliage is likewise diminutive, as com- 

 pared witli the branches. The forest was almost 

 composed of the kauri, and the largest, from the 

 parallelism of their sides, stood up like gigantic 

 columns of wood. The timber of these trees is 

 the most valuable product of the island ; more- 

 over, a qxiantity of resin oozes from the bark, 

 which is collected, and sold at a penny a pound 

 to the Americans, but its use is kept secret." 



Trees, when placed in suitable soil, and in a 

 situation adapted to their nature, are capable of 

 living for centuries. Thus the olive-tree may 

 continue for 300 years, and the oak about 600. 

 The cedars of Lebanon seem in a manner in- 

 capable of decay. According to very ingenious 

 calculations, Adanson supposed that the baobab 

 might be many thousand years old. 



In dicotyledonous trees, the age may be known 

 by the number of woody layers which a trans- 

 verse section of the trunk presents. As a new 

 layer of wood is formed every year, it will easily 

 be seen that a tree twenty years old, must pre- 

 sent at its base twenty concentric rings of wood, 

 and so on successively. In the trees of tropical 

 climates, however, this annular indication is 

 less to be depended upon, and may, as in the 

 case of the baobab, lead to erroneous conclusions. 



Uses of stems. Wood is applied to so many 

 uses in domestic economy and the arts, and is 

 so indispensable in the construction of ships and 

 buildings of all kinds, as well as of machines 

 and instruments, that no part of vegetables can 

 dispute the superiority with it in this respect. 



Many herbaceous stems are employed as food 

 for man and animals. The stem of the sugar- 

 cane supplies most of the sugar of commerce. 

 Many woods are used for dyeing : for example, 

 sandal-wood, logwood,brazLl-wood, &c. Leather 

 is tanned with oak-bark, and, in general, with 

 those kinds of bark which contain a great 

 quantity of tannin. 



With respect to medical properties, the stems, 

 the wood, and the bark, are of essential impor- 

 tance. To these belong the cinchonas, cinnamon, 

 winter's-bark, sassafras, guyacum, and many 

 other medicines which possess so well-merited a 

 reputation. 



Various operations are often practised on the 

 trunks of trees. Incision is sometimes neces- 

 sary to the health of the tree, in something 

 of the same way as bleeding is to the health 

 of nn over full animal. The trunk of the 



plum and cherry tree seldom expand fi-eely 

 till an incision is made lengthwise along the 

 trunk, and hence this operation is often prac- 

 tised by gardeners. If the incision only extends 

 through the epidermis, it heals up without 

 leaving any scar ; if it penetrates into the interior 

 of the bark, it heals up only by means of leaving 

 a scar ; but if it penetrates into the wood, the 

 wood itself never heals up completely, but 

 new wood and bark are formed above it. 

 Boring is an operation to which the trunks 

 of trees are often submitted, for the purjwse of 

 making them part with their sap in the season 

 of their bleeding, particularly the birch and the 

 American maple. A horizontal, or rather slanting 

 hole, is bored in them with a wimble, so as to 

 penetrate an inch or two into the wood ; from 

 this the sap flows copiously, and though a num- 

 ber of holes is often bored in the same trunk, 

 the health of the tree is not materially, if at all 

 affected ; for trees will continue to thrive though 

 subjected to this operation for many successive 

 years, and the hole, if not very large, will close 

 up again like the deep incision, not by the union 

 of the broken fibres of the wood, but by the 

 formation of new bark and wood projecting be- 

 yond the edge of the orifice, and finally shutting 

 it up altogether. Girdling is an operation to 

 which trees in North America are often sub- 

 jected, when the farmer wishes to clear his land 

 of timber. It consists in making parallel and 

 horizontal incisions with an axe into the trunk 

 of the tree, and caiTying them quite round the 

 stem, so as to penetrate tlirough the alburnum, 

 and then to scoop out the intervening portion. If 

 this operation is performed early in the spring, 

 and before the commencement of the bleeding 

 season, the tree rarely survives it ; though some 

 trees that are peculiarly tenaceous of life, have 

 been known to survive it for a considerable 

 length of time. If a tree is bent so as to break 

 part only of the cortical and woody fibres, and 

 the stem or branch is but small, the parts will 

 again unite by being put back into their natural 

 position and well propped up, especiaUy if the 

 fracture occurs in spring, when the juices are 

 in abundance ; but it will not succeed if a con- 

 tusion has crushed and destroyed the vessels ; 

 or if the stem is very large, even where it suc- 

 ceeds, the woody fibres do not conti-ibute to the 

 union, but the herbaceous substance only, which 

 exudes from under the liber, and which insinu- 

 ates itself tlirough all the interstices. In prun- 

 ing for repressing the excessive growth of 

 branches, a slanting division of the branch is 

 made close to the trunk ; in this case the wound 

 soon closes uj) by the meeting of the opposite 

 sides of the cut bark. 



