LECT. III.] THE SAP. 113 



the hydrogen and oxygen may be obtained, and the 

 carbon from the acetate of potash and carbonate 

 of lime ; Vauquelin was authorized in concluding 

 that the acetate and carbonate, which are found in 

 a diminished quantity in sap drawn at an advanced 

 season, may be decomposed by the vital action of 

 the growing plant, and the carbon they yield with 

 the hydrogen and oxygen go to form the vegetable 

 matter. But although the acetates are found in 

 soils, yet they are not in any considerable quantity, 

 nor sufficient to supply all the carbon wanted for 

 the purposes of plants : it is, therefore, probable 

 that if sap could be examined in its purest state, 

 it would be found to consist of water, holding car- 

 bonaceous matter in solution, acetate of potash, 

 carbonate of lime, and now and then some siliceous 

 and aluminous particles, suspended in the so- 

 lution, and of sufficient minuteness to enter the 

 mouth of the absorbents of the root. It is pro- 

 bable, also, that there is little difference in the 

 pure sap of all plants ; but as the first changes 

 take place undoubtedly in the roots, and the modi- 

 fying power of these parts must be different in 

 different kinds of plants, the changes which occa- 

 sion the varieties of the sap, are sooner produced 

 in some plants than in others. On these differences 

 of the ascending fluid, however, the secretions 

 certainly do not depend ; for, if that were the case, 

 the grafted branch would not bear fruit and leaves, 



VOL. I. I 



