PHYSIOLOGY OF TREES. 253 



many circumstances which militate against such 

 doctrine. 



It is always considered, in practice, that ma- 

 tured sap is one thing, and organisation is 

 another. If they be the same thing, they will 

 invariably produce the same effects in all similar 

 cases ; at least we should expect so. But that 

 this is not the fact, the following instances will 

 show : — 



Choose, from a well-ripened healthy shoot of 

 a grape-vine, an internode piece, that is, a piece 

 deprived of its nodes or joints. After ascertain- 

 ing that it is perfectly sound wood, and of course 

 fully charged with matured sap, let it be planted 

 as a cutting in the most favourable situation, 

 affording it every assistance from artificial heat, 

 and every other auxiliary means that practical 

 experience can devise. Will this repository of 

 perfect sap ever produce a shoot? No, never; 

 temporary rootlets may be produced ; and though 

 the cambium may be put in motion, and even 

 show its callosities at each end, nothing like a 

 shoot will ever come forth. Again, tubers are 



