J S6 PROCESS OF NUTRITION. CHAP. III. 



ducts it in its descent from the summit of the leaf 



down to the base of the foot-stalk.* 



Channel But by what means js the proper juice conducted 

 veyance from the base of the leaf-stalk to the extremity of 



thestem. the rOot ? This Was the cbief ob J ect f the in q uir 7 

 of the earlier phytologists who had not yet begun to 



trace its progress in the leaf and leaf-stalk ; but who 

 were acquainted with facts indicating at least the 

 descent of a fluid in the trunk. If the stem, or 

 branch, or even root of a woody plant is encircled 

 , by a strong ligature, a tumor is formed immediately 



above the ligature, but no tumor is formed below 

 it.^ Hence they inferred the descent of a fluid 

 that was now stopped ; but this descending fluid was 

 proved also to be the Cambium or proper juice. If 

 a branch of any tree abounding in a conspicuous 

 proper juice, such as the Fig or Fir-tree, is cut 

 transversely in two, the proper juice will flow much 

 more copiously from the upper portion next the 

 leaves than from the under portion next the trunk, 

 even though their positions should be inverted. If 

 trees are stripped wholly of their bark, they will 

 often form new productions from the leaf down- 

 wards, but none or scarcely any from the root up- 

 wards. Du Hamel stript GO trees of their bark in 

 the course of the spring, laying them bare from the 

 upper extremity of the sap and branches to the 

 root ; the experiment proved indeed fatal to them, 

 as they all died in the course of three or four years. 

 * Phil. Trans. 1806. t Phys. des Arb. liv. v. chap, ii. 



