APPENDIX. 109 



size of the pores in their roots, by which they re- 

 ceive their several nourishments. 



11 Secondly. We must observe that the wood of 

 every plant is composed of capillary tubes, run- 

 ning parallel with each other from the root (up- 

 right) through the trunk. Their cavities are so 

 small that they are hardly to be discerned by the 

 natural eye, unless in a piece of charcoal, cane, 

 or oaken board. These vessels renew and aug- 

 ment themselves every year, as we may observe 

 by cutting a tree horizontally, which will dis- 

 cover to us the latitudinal shootings and the an- 

 nual additions of these pipes, and for which rea- 

 son the trunks of trees increase in their circumfe- 

 rence. These tubes, for distinction sake, I shall call 

 arterial vessels, for it is through these the sap rises 

 from the root in fine vapour, for their cavities are 

 so small that it would be impossible they should 

 admit anything whose parts were so large as those 

 of a liquor. 



" Thirdly. The passages or pipes by which the 

 sap returns downward are much more open than 

 the former, and are capable of receiving a liquor 



