RAY. 37 



of the sap In trees ; and the result of their inquiries, 

 communicated to the Royal Society, appeared soon 

 after in the " Philosophical Transactions." Their 

 experiments clearly prove the ascent of the sap 

 tiirough the woody part of the tree, which is easiiy 

 detected by boring the trunks at different depths 

 before their leaves are unfolded; and they observed, 

 also, the mucilaginous nature of the flowing sap, 

 " precipitating a kind of white coagulum or jelly, 

 which," says Ray, in a note preserved by Derham, 

 " may be well conceived to be the part, which every 

 year, between bark and tree turns to wood, and of 

 which the leaves and fruits are made. And it seems 

 to precipitate more when the tree is just ready to 

 put out leaves and begins to cease dropping, than 

 at its first bleeding." The accuracy of the leading 

 facts recorded by these ingenious men is confirmed 

 by subsequent observers, who have further pursued 

 the same subject, which is now sufficiently well 

 understood. The sap originates in the liquid v^ 

 matters which are absorbed by the roots of plants ; \ 

 they enter the minute cells of the ends of the 

 roots and permeate the cellular tissue. This sap 

 ascends in the plant, assisted by the evaporation 

 from the leaves. The sap ascends with consider- 

 able rapidity to the leaves, where it is subject to 

 changes, the result of physiological action. It 

 descends from the leaves, having had its chemical \ 

 constitution altered, and is fit for the nutrition of 

 the plant. The sap ascends through the cellular 

 and woody tissue, especially in the layers of wood 



