fcOTANY. 



pulpy texture, and the seat of colour. It 

 is commonly green in the leaves and 

 stems, and is dependent for its hue on the 

 action ot'light. 



When the cellular integument is re- 

 moved, the outer surface of the bark pre- 

 sents itself, which in plants or branches 

 that are only one year old, consists of one 

 simple layer, often scarcely separable 

 from the wood. In the branches and 

 stems of trees it consists of as many lay- 

 ers as they are years old ; the innermost 

 of these is called the liber, or inner bark, 

 in which the vital functions for the sea- 

 son are carried on, and in the meanwhile 

 materials for the new liber are secreted 

 and deposited on the inside ; the latter is 

 destined to perform the requisite func- 

 tions in the ensuing spring, when the last 

 year's liber is united and assimilated to 

 the outer bark, as its predecessors had 

 been. It appears also, from the experi 

 ments and observations of Duhamel, 

 Hope, Knight, and others, that the liber 

 deposits matter also for a new layer of wood. 

 The bark owes its strength and tenacity 

 to innumerable wood) fibres, mostly 

 longitudinal, though connected laterally, 

 so as to make a kind of net-work. This 

 reticulation is so perfect and beautiful 

 in the daphne laghetto, or lace bark of 

 the West Indies, that it may be stretch- 

 ed laterally into a kind of gauze, some- 

 times used for articles of ornamental 

 dress. The bark contains, in appropriate 

 vessels, the principal secreted fluids of 

 trees in great perfection. Its medicinal 

 virtues in many instances are familiar to 

 us ; the Peruvian bark affords " a cooling 

 draught to the fevered lip ;" while that 

 of the cinnamon yields a rich cordial ; that 

 which is stripped from the oak is used 

 for the purpose of tanning, for which se- 

 veral other kinds are of inferior utility. 

 When a wound is made in the bark, it 

 heals, though slowly, by the lateral exten- 

 sion of the portion which is left. 



Immediately under the bark is situated 

 the -wood, which forms the great bulk of 

 trees and shrubs. This also consists of 

 numerous layers, as any one must have 

 observed in the fir and many other trees. 

 Each of these layers is moreover com- 

 posed of other thinner ones ; their sub- 

 stance consists of innumerable woody fi- 

 bres, and is perforated by longitudinal 

 sap-vessels, variously constructed or ar- 

 ranged in different trees, and intermixed 

 with other vessels containing secreted 

 fluids or air. 



It would be superfluous to enlarge on 

 the economical uses of wood in everv 



country, from the most barbarous to the 

 most refined. Of this material the savage 

 forms his club and his spear, while the 

 civilized part of mankind convert it to the 

 purposes of comfort and luxury. Many 

 conjectures iiave arisen among philoso- 

 phers, with respect to the manner in 

 which the circular layers of wood are an- 

 nually formed, and the effects which heat 

 or cold may have on their formation. Cold 

 seems to condense the operation, as well 

 as for a time to interrupt it ; since in the 

 trees of hot countries these rings or lay- 

 ers are scarcely perceptible. In many 

 trees more or less of he outermost lay- 

 ers continue for a time of a different co- 

 lour and texture from the inner ones, and 

 are called by workmen the sap. Such 

 layers are unfit for any lasting service. 

 The laburnum shews them very distinct- 

 ly, and the oak likewise. It was long a 

 matter of great uncertainty, how, or 

 whence, each new lav er of wood was add- 

 ed to the former ones. Malpighi and 

 Grew, the first physiologists who gave at- 

 tion to the subject, formed, without 

 any mutual communication, an opinion, 

 which proves to be correct, and to which 

 we have already alluded, that the bark de- 

 posited every year from its own substance 

 a new layer of wood. Hales thought this 

 new layer proceeded from the wood of 

 the former year ; Linnaeus presumed that 

 it was secreted, internally, next to the 

 pith. The experiments of Duhamel and 

 Hope confirmed the sentiments of Grew 

 and Mulpighi ; and at present there is no 

 kind of doubt upon this subject. A layer 

 of wood being formed every year, it is 

 evident that the age of a sound tree may 

 be known from counting its rings when 

 felled ; and it has been observed, that 

 hard winters are recorded in this natural 

 register by certain rings being more 

 dense than the rest. In the north side of 

 a tree also they are usually more narrow 

 than on the south ; and upon this princi- 

 ple a mode for travellers to find their way 

 through an unknown forest has been sug- 

 gested, namely, that by felling a tree they 

 might ascertain the points of the compass ; 

 but we humbly conceive that much more 

 obvious means for the same purpose are 

 within the reach of every traveller, and 

 that the one recommended is somewhat 

 like telling 



" That hour of the day 



The clock doth strike by algebra.'* 



Within the centre of the wood is the 

 med-ulla, or pith, which is a cellular sub- 



