( 13 ) 



The filTure or fplitting of the particle of wood, reprcfented in 

 fig.^, was in fuch a direftion that, as I may fay, it palled or took 

 its dTe6lion through the center of the tree, by whicli means the 

 horizontal vellels, as well as the perpendicular ones, were divided 

 longitudinally, and therefore are both exhibited in the fame Fgure. 



Between K I and H G, the horizontal tubes or velTels are repre- 

 fented when divided longitudinally. Thefeveflels a,re Ibund in great 

 abundance in this wood, and in fome places fix, feven, or even. twelve 

 of tliem fliall be found clofe together, and it is very rare to fee fo 

 large a fpace of tiie perpendicular ved'els without horizontal ones, as 

 is between G and F in this figure, though the real fizeof that fpace 

 is not more than the thicknels of a large grain of fand. 



I have often refle6led on the nature of thefe horizontal vellels, 

 that is, how they are formed, and how fupplied with nutritive juices^ 

 for through them a new coat of bark is every year pi'oduced round 

 the tree. At firft, they undoubtedly have their rife from the mar- 

 row or pitli in the center, but afterwards they mult necellarily pro- 

 ceed from the afcending vellels. In this enquiry I could not fully 

 fatisfy myfelf, except tliat I obferved the appearance of certain 

 fmall dots or points in many parts of the perpendicular vellels, which 

 at length I difcovered to be no other than fmall round apertures. 

 Thefe are reprefented in fg. 8, between B C, and G H, and as I did 

 not fee them in any other places than where 1 had clivided the hori- 

 zontal from the afcending vellels, I concluded that at thefe fmall 

 apertures the horizontal velTels are united to the perpendicular ones. 

 And I began to ccnfider whetiier the afcending tubes were not air 

 vellels, as well as inftrumental in conveying the nutritive juices. 



I then fat about a more accurate examination of this wood, by 

 cutting off thin flices with the fharpeft et^ged tools I could procure, 

 and placed them before the microfcope, and hereupon I difcovered 

 a much larger number of afcending vcileis than I had before 



