ASCENT OF THE SAP. 25 



the buds, which it is to supply with nourishment. 

 During this circuitous passage, it probably un- 

 dergoes a certain degree of elaboration, fitting it 

 for the office which it has to perform : it appa- 

 rently combines with some nutriment, which had 

 been previously deposited in the plant, and which 

 it again dissolves ; and thus becoming assimilated,, 

 is in a state proper to be incorporated with the 

 new organization that is developing. This nurs- 

 ling sap, provided for the nourishment of the 

 young buds, has been compared to the milk of 

 animals, which is prepared for a similar purpose 

 at those times only when nutriment is required 

 for the rearing of their young. 



Several opinions have been entertained with 

 regard to the channels through which the sap is 

 conveyed in its ascent along the stem, and in 

 its passage to its ultimate destination. Many 

 observations tend to show, that, in ordinary cir- 

 cumstances, it is not transmitted through any of 

 the distinguishable vessels of the plant : for most 

 of these, in their natural state, are found to con- 

 tain only air. The sap must, therefore, either 

 traverse the cells themselves, or pass along the 

 intercellular spaces. That the latter is the 

 course it takes is the opinion of De Candolle, 

 who adduces a variety of arguments in its sup- 

 port. The sap, he observes, is found to rise 

 equally well in plants whose structure is wholly 

 cellular ; a fact which proves the vessels are not 



