66b 



Microscopical Essays. 



of filaments, interwoven together in various directions ; it is 

 more abundant in fome trees than in others, particularly in -the 

 elder, and more fucculent in fummer than in winter; it is then 

 alfo lefs adherent to the rind. Dr. Hill thinks the beft time of 

 feparating the rind, in order to view this part, is in a living 

 branch, at the time of it's fwelling for the fpring, or for the mid- 

 fummer fhoot, but much eafier by the means of maceration.* 



When the rind is perfectly feparated, it leaves the vafa propria 

 of this clafs behind it; they fcarce adhere to the inner bark, and 

 but little to the rind ; they are difpofed in packets, and do not. 

 run ftraitdown the branch, but interweaving with each other form 

 a kind of net. Thefe packets may be feparated eafily from the 

 bark ; when a thin tranfverfe fection of one of them is examined,, 

 it is found to be compofed of twelve or fifteen diftincl; veflels^ 

 with hard rinds. Dr. Hill fays, that with a great deal of patience,, 

 a vaft number of objects, and a good microfcope, ,we may fee by 

 what means thefe veffels adhere to the bark ; for we fh all rind > 

 upon the fides fmall oval depreffions which fit thereto, and that 

 are probably a kind of glands, that feparate from the general 

 More of fap with which the bark is filled*- the juices peculiar to. 

 thefe veffels. 



Of the Bark. 



The bark lies next within the rind, and differs but little from k 

 in conflru&ion, though it holds a more important office in the 

 fcale of vegetation, the growth and qualities of the tree being in 



a great 



* Hill's Conftru&ion of Timber, p. 75. 



