88 
WOOD AND BARK OF TREES. 
Formation of 
the wood. 
Net of the 
■wood all spiral 
wire. 
Root; perpe- 
tual moth n in 
the interior. 
Capillary at- 
traction helps 
I shall now begin with the dissection of the wood of the root. 
It may be said to consist of four parts ; fig. 1. The sap vessels, 
which are large simple cylinders, without any division 3 B. the 
net in which they are inserted 3 C. the bastard vessels ; 13 . the 
silver grain which marks each yearly circle 5 the sap cylinders 
engross much the largest part of the root ; for though it is not 
such an absolute sponge as the radicles ; yet the apertures are 
very closely placed, so as often to break into each other 3 see 
fig. 2, when the layers are cut very thin, to form transparent 
images of the parts. It was with great astonishment that I dis- 
covered the excessive motion of the root, and the folds which 
appertained to it 3 but had I then been apprized of the nature 
of the net, I should have known that it was but the necessary 
consequence of its formation 3 upon placing some very old vege- 
table cuttings of the root in my sliders, and exposing them to 
the highest magnifying powers I possessed, I found that almost 
every part of the net was composed of spiral wire in its cases 5 
and as the cases in many parts had broken away, all the interior 
was become visible 3 this has made me dissect many woods, and 
I find that it is the same in all 3 that not only the greatest part 
of the net is so formed, but that the spiral vessels surround each 
sap vessel, first extremely tight at the edge, reducing or enlarg- 
ing the aperture, and then a little beyond it, forming a kind of 
scollop, besides large coils of the same, passing from one aper- 
ture to another, see A, EE, like those which surround the bas- 
tard vessels, and mark all the folds. The wood may be truly 
said, therefore, to be little else but spiral wire, and to be perpe- 
tual motion in the interior, the effect of the quantity of those 
vessels that pervade it. This shews of what consequence dis- 
section is, and that, by banishing all imaginary causes, and 
letting nature herself shew her own works, and be merely the 
transcriber of the information she gives, by degrees every cause 
will be discovered 3 when I found out that the root possessed 
such motion, I had no idea the net was formed by the spiral 
wire 3 but I was resolved to take each thread to pieces 3 to see 
and comprehend its texture ; and, surely, this perpetual motion, 
aided by capillary attraction, is quite sufficient to account for 
the rising of the sap. 
Three years ago, I dedicated a whole winter to the study of 
capillary attraction 3 and I found that the smaller the vessels, 
the 
