SECT. VIII. DESCENT OF PROPER JUICE. 187 



But many of them had made new productions both 

 of wood and bark from the buds downwards, ex- 

 tending in some cases to the length of a foot ; though 

 very few of them had made any new productions 

 from the root upwards. Hence it is that the 

 proper juice not only descends from the extremity 

 of the leaf to the extremity of the root, but gene- 

 rates also in its descent new and additional parts. 



But although the above experiments prove in 

 general the descent of the proper juice, yet they do 

 not decide in particular by what peculiar channel it 

 descends that is, whether by the bark or wood. 

 It was the opinion of Du Hamel that it descends According 

 through the channel of the bark, in favour of which JJ 

 there is indeed an original presumption in the fact 

 of its being always found in the greatest abundance 

 in the bark when analysed ; or of its flowing the 

 most copiously from it when cut ; as well as a 

 direct and positive proof in the result of the follow- 

 ing experiments : In the time of the flowing of the 

 sap Du Hamel stripped the trunk of a Cherry-tree of 

 a ring of bark, and covered the wound with a piece 

 of canvass to let nothing escape, wrapping it up at 

 the same time with an additional covering: of straw 



o 



to prevent its becoming dry : the result was that 

 the upper lip yielded a most copious exudation of 

 gum, while the lower lip yielded none ; but the tree 

 did not long survive the experiment. The proper 

 juice then descends through the channel of the bark, 

 and cannot be made to descend through the medium 



