AGRICULTURE AND PLANTING. , 3 



On the Structure oj Vegetables. 



pletely elaborated. By this elaboration, those chemical principles are selected 

 which can alone contribute to.the sustenance of vegetable lijfV. 



3. The Libej', oi inner bark, is membranous, flexile, and sometimes wholly 

 separable from the cortex and alburnun:^ These two coats of a tree, namely, th^ 

 cortex and liber, are formed of lamina;, as will appear by macerating them injjra* 

 ter; by which the cellular sUbstarice is destroyed, and the laminkted appearahc« 

 becomes conspicuous. They appear to be parts very essential to the life of the 

 vegetable,, for in them the principal functions of life^ as nutrition, digestion, se- 

 cretion, &c. are performed; as is evinced in those trees whigh are hollow within, 

 and plants which are kept in vigour by the good state of their barks, although 

 rotten internally. Of this kind of hollow tree a remarkable instance remains in 

 Welbeck Park in Nottinghamshire, through the middle of which a coach is said 



to have been driven. The cortical coverings are easily detached from each other; 



■ ■ ■ ( 



and it is fromlheir gross resemblance to the leaves of a book, that they have beeii 

 called liber. 



4 The Alburuum, is the nex^ integument to the liber, situated between it 

 and the wood, composed of a soft whitish substance, not easily discernible in some 

 trees; but in the oak &ndelm it is harder and more apparent. It is, as it were, an 

 imperfect wood ; not having acquired the degree of consistence proper to perfect 

 wood ; it is that state between bark and wood, that the former niust necessarily 

 arrive at, before it can become the latter. The hardness of the alburnum is in 

 proportion to the vigour of the plant. 



The vessels, which convey the sap-jliice with such amazing force, are situated 

 in or compose the alburnum, or sap-wood, of the trunk or root of trees, nor is it 

 surprising, that some of it when pressed by so high a column should exude into 

 the cells between the alburnum and bark. That the vessels of the alburnum in 

 their living state possess the property of conveying the sap juice, which is pra- 

 pelled upwards in the early spring by the absorbent terminations of the rootfe, 14 ,. 

 visible in decorticated oaks; the absorbent mouths of these sap-vessels open exter- 



