( 4 ) 



they are reprefented as feen by the naked eye, in Jig. s, RS,) and 

 ■where they are reprefented magnified and feen longitudinally in 

 Jig. 3, I have in many places drawn crofs lines, to reprefent what I 

 conceive to be minute valves, and though I could not fee them fodif- 

 tindrly, as here they are drawn, yet I cannot doubt of their exiftencc, 

 having frequently feen thefe valves in other woods, and particularly, 

 very dlftinftly in the Elm ; befides, it feems evident to me, that 

 without fuch valves the tree could not be increafed in its bulk, on 

 account of the great force required to feparate and loofen tlie bark 

 from the tree, in the time of fpring, and alfo for the violent burft- 

 ing open of the bark, to allow for the growth and increafe of the 

 wood: and if there were not fuch valves, the juices, which by the 

 a6lion of the fun are drawn outwards, would, at iun fet, when that 

 motion of the juices ceafes, be drawn back again, and their exer- 

 tions to diflend the bark become fruitlefs. A portion of thefe veflels 

 is reprefented in /;g. 4,, TV, which figure is drawn from a microfcope 

 of greater magnifying power than that from which the perpendicu- 

 lar veflels are drawn, in order that thefe horizontal ones may be 

 more clearly feen: and in this fmall piece of wood, and in this little 

 fpace, which is no more than the feven hundredth part of a fquare 

 inch, are more than two thoufand veflels. 



It is well known that there is a great difference in Oak Timber, 

 namely, whether it grew in mountainous Situations, or low lands, and 

 whether in warmer or colder climates, and laftly, whether it was of 

 quicker or flower growth. As to the fpecimen of Oak which has 

 been juft defcribed, it was taken from a tree of thebeil quality, very 

 compact and clofe grained, and which had been very flourifhing in 

 its growth. 



Oak timber of this fuperior quality we mufl: not expeft to find in 

 the Northern or cold countries, but in the warmer ones. The very 

 befl: timber that we have here, in Holland, is brought down thco 



