124 PROCESS OF NUTRITION. CHAP. III. 



also further elucidated by means of direct expe- 

 riment. Du Hamel having selected a tree for the 

 purpose of experiment, made two incisions at dif- 

 ferent heights and on opposite sides of the trunk, 

 each penetrating to the centre. He then closed up 

 the gaps with a mixture of wax and turpentine, in 

 order to prevent the action of the air from inter- 

 fering in the result ; and found accordingly that the 

 tree continued to vegetate as before the experiment. 

 Hales took two branches of equal size, in one of 

 which he made four incisions, answering to the 

 four cardinal points, and each penetrating to the 

 centre ; in the other he made no incision. He 

 then put the extremities of both into water, and 

 found that the branch that was cut with incisions 

 absorbed moisture as copiously as the one that was 

 not so cut. Knight has also shown that a branch 

 will still continue to live though the tubes leading 

 directly to it are cut in the trunk.* From all which 

 it follows that the sap, though flowing the most co- 

 piously in the direct line of ascent, is at the same 

 time also diffused in a transverse direction. But 

 this seems to have been acknowledged even by 

 Grew himself, in spite of all he has advanced in 

 support of a contrary opinion : for he says that 

 the sap vessels of the bark being the first year ad- 

 jacent to the pith, do all that time transfuse part 

 of their sap into it, and so keep it always succu- 

 lent;^ which, whether we regard as being the fact 

 * Phi). Trans. 1801. t Vcg. of Trunks, chap. i. 



