108 PROCESS OF NUTRITION. CHAP. Ill, 



According Grew has shown this opinion to be altogether er- 

 roneous, and has substituted a third in its place 

 namely, that the sap ascends by the bark, wood, and 

 pith indiscriminately.* It ascends by the pith, as 

 he says, during the first year of the plant's growth, 

 and during the first year only ; because the pith is 

 always found succulent during that time., whether in 

 the sprout from a seed, or sucker from a root, or 

 scion from a branch ; but dry ever after. And it 

 ascends by the wood and bark, because upon cutting 

 a branch a liquid issues from both either spontane- 

 ously or by pressure. But we must not too hastily 

 conclude that any particular part of the plant serves 

 as the channel of the sap's ascent, merely because 

 it has been found to be moist, or to give out a liquid 

 by pressure ; for one might just as well say, because 

 the soil of a meadow situated bv the banks of a 

 river contains a great deal of moisture, that it is 

 therefore the channel of the descent of the water as 

 well as the bed of the river itself. The sap is no 

 doubt conveyed to all the parts of the plant, and is 

 consequently to be found in them all under one 

 modification or another, but still its ascent is con- 

 fined to a peculiar channel. Let us try to ascertain 

 by experiment what that channel is. 



If a tree is to be subjected to the operation of 



bleeding, there will be no notable discharge of sap 



unless the bore or incision penetrates beyond the 



bark ; and if the operation is performed on the 



* Vcg. of Trunks, chop. i. 



