HI 



culiar organs, assumes the particles suitable to its own ' 

 nature, letting the rest pass OQ through the common 

 ducts. 



11. As to the motion of the nutritive juice, some 

 think it ascends by the wood, and descends by the 

 bark. Bit it is not easy to shew by what particular 

 tubes it either ascends or descends. Neither after all 

 our researches does it appear what is the principle of 

 this motion? Whether there be any such thing as an 

 attractive force in the plant itself, or whether it be 

 performed on the mere principles of mechanism, by 

 the expansion of the air contained in the juice, whjch 

 moves and propels the particles of it into every part of 

 the plant ? 



However, that the 'sap in plants does circulate is 

 made probable by an easy experiment. On a branch 

 of a plain jessamine, whose stem spreads into two or 

 three branches, inoculate in autumn, a bud of the 

 yellow striped jessamine. When the tree shoots the 

 next summer, some of the leaves will be striped with 

 yellow, even on the branches not inoculated, and by 

 degrees the whole tree will be striped, yea, the very 

 wood of the young branches. 



It is probable the circulation is performed thus : the 

 wood of plants consists of fine capillary tubes, which 

 run parallel with each other from the root, and may 

 be looked upon as arteries. On the outside of these, 

 between the wood and the inner bark, are larger tubes, 

 whkh may do the office of veins. Now the root having 

 imbibed juice from the earth, this is put into motiou 

 by the heat. Hereby it is rariiied and caused to as- 

 ceud in the form of a steam or vapour, till meeting 

 the mouths of the arterial vessels, it passes through 

 them to the top, and to the extreme parts of the tree, 

 with a Corce answerable to the heat whereby it is 

 moved. When it arrives there, meeting with the cold 

 of the external air> it condenses into a liquor, a ,d in 

 that form returns by its own weight to the root of the 

 tenal vessels. 



