FRANCIS WILLUGHBY. 81 



In the spring of the year 1669, Mr Willughby 

 and Mr Ray entered upon a course of inquiries 

 into the theory of vegetation. They first de- 

 voted their attention to the motion of the sap 

 in trees; the results of their inquiries were 

 communicated to the Royal Society, and appeared 

 soon afterwards in the Philosophical Transac- 

 tions. The probable reason why they did so 

 was, the discovery of the circulation of the blood 

 in animals, published only about forty years before 

 by Dr Harvey, although he had for some years 

 taught the doctrine in his lectures to his pupils. 

 They perhaps expected to find something equi- 

 valent in the constitution of plants. 



The experiments made at that early period of 

 the investigation may be perused with interest. 

 It was considered that the following facts were 

 established : " That the sap of any tree, running 

 down the side of it, or dropping on one place, will 

 precipitate a kind of white coagulum or jelly ; 

 and this, it was imagined, might be the part 

 which every year, between bark and tree, turns 

 to wood, and of which the leaves and fruit are 

 made. 



" That a tree precipitates more when it is just 

 ready to put forth leaves, and is about to cease 

 dropping, than at its first bleeding : that the sap 

 ascends, not only between the bark and the tree, 

 but by all the pores of the wood. This was 

 thought to be undeniably proved by boring in 

 the same tree, just before the expansion of the 

 leaves, holes of different depths, or the same hote 



