VOL. XIII.] PHILOSOPHICAL TRANSACTIONS'. 621 



the sun, when I conceive the sap ceases to rise,* would fall back again, and cause 

 a labour in vain. In this small piece of wood TV, fig. 4, (described by a mag- 

 nifying glass which augments more than that by which the ascending vessels are 

 drawn, that so the vessels might appear more distinct) there are more than 

 2000 vessels, each of which, if it be allowed but -\- of a grain of force in the 

 protruding its moisture, the force which all these horizontal vessels together 

 must use towards the separation of the bark from the wood, will appear by this 

 calculation. Suppose then that fig. 4 is ^y-S-g- of a square inch, and that in the 

 whole piece are but 2000 vessels, which make in a square inch 1,400,000 ves- 

 sels, that is 350,000 grains; this number divided by 10,240, the grains in a 

 pound, makes full 34 pound, for the force which the vessels in so small a piece 

 of wood come to exercise upon the bark. 



In fig. 6, ABCD, is represented a piece of elm-wood, which to the naked 

 eye is the size of fig. E, and is what this tree increased in one year in thickness. 

 AD and BC show the ceasing of the growth in the year's end. The small 

 rising vessels, which lie together between the great vessels, are in this wood 

 smaller than in oak, and each pipe consists of a thicker film than the pipes of 

 the oak. AB and CD show the horizontal vessels at full length. 



Fig. 7, FFFF show the horizontal vessels cut across; of which, those that 

 lie but few together, I conceive to be vessels lately proceeding out of the rising 

 vessels : whereas on the contrary, the other vessels which lie many together, 

 have subsisted many years, and are as many in number as they ever will be. 

 GGGG show the small rising vessels at length. 



HH show one of the great rising vessels in length, cut cross in the middle; 

 yet when we observe the same more exactly, we see that they consist of very 

 thin films, beset with helical threads, exhibiting obscure spots on the bends, 

 fig. 3. 



Among these trees there are several which upon tapping yield a sap. This 

 sap I have several times, and several years observed, and taken notice in it of 

 divers small animals, which I could not imagine should have come out of the 

 wood, but rather that they might have come from rain water or dew. 



Fig. 8, ABCD is a piece of beech, as large as fig. F to the naked eye, the 

 thickness of one year's growth ; wherein one may plainly see at AD or BC the 

 beginning and end of the year's growth. In this wood there are represented 

 two sorts of rising vessels, viz. greater and smaller; and I imagine that there are 

 also two sorts of horizontal vessels, which are very small : one of which, viz. 

 EEE lies but 1, 2, 3, or more together, as fig. 9, which shows those vessels 



* Yet vines and other plants bleed day and night. 



