43 



CHAPTER VIIL 



OF THE SAP-VESSELS, AND COURSE OF 



THE sap; with Mil. knight's theory 



OF VEGETATION* 



jVlucii contrariety of opinion has existed 

 among physiologists concerning the vascular 

 system of plants, and the nature of the pro- 

 pulsion of the sap through their stems and 

 branches. Indeed it is a subject upon which, 

 till lately, very erroneous ideas have pre- 

 vailed. 



That the whole vegetable body is an as- 

 semblage of tubes and vessels is evident to 

 the most careless observer; and those who arc 

 conversant with the microscope, and books 

 relating to it, have frequent opportunities of 

 observing how curiously these vessels are ar- 

 ):anged, and how different species of plants, 



