78 SAP. 



sap continued to rise, and the portion above the incis- 

 ion augmented as usual, while the portion below the 

 ring scarcely augmented at all. " But if a bud was pro- 

 truded under the ring, and the shoot arising from it 

 allowed to remain, then the portion of the trunk below 

 that bud began immediately to augment in size, while 

 the portion between the bud and incision remained 

 nearly as before. When two circular incisions were 

 made in the trunk so as to leave a ring of bark between 

 them, with a leaf growing from it, the portion above 

 the leaf died, while the portion below the leaf lived ; 

 and when the upper part of a branch was stripped of 

 its leaves, the bark withered as far as it was stript. 

 Whence it is evident that the sap which has been 

 elaborated in the leaves and converted into proper 

 juice, descends through the channel of the bark, or 

 rather between the bark and alburnum to the extremi- 

 ty of the root, effecting the developement of new and 

 additional parts. 



But not only is the bark thus ascertained to be the 

 channel of the descent of the proper juice, after enter- 

 ing the trunk ; the peculiar vessels through which it 

 immediately passes, have been ascertained also. In 

 the language of Mr. Knight they are merely a continua- 

 tion of the external tubes already noticed, which after 

 quitting the base of the footstalk he describes as not 

 only penetrating the inner bark, but descending along 

 with it, and conducting the proper juice to the very 

 extremity of the root. In the language of M. Mirbel, 

 they are the large or rather simple tubes so abundant 

 in the bark of woody piants, though not altogether con- 

 fined to it ; and so well adapted by the width of their 

 diameter, to afford a passage to the proper juice." 5 * 



* Keith. 



