112 THE SAP. [LECT. HI. 



acetate of lime, sugar, mucilage, vegetable ex- 

 tract, and water. In the sap of the Common 

 Birch, Betula alba, he found acetate of lime, 

 acetate of potash, acetate of alumina, sugar, vege- 

 table extract, and water. In all the specimens thus 

 analysed the quantity of vegetable matter was 

 found to be greater in the sap drawn late in the 

 season, than in that collected at an earlier period 

 of it. 



If we are to consider these results of Vauque- 

 lin's experiments as pointing out the real composi- 

 tion of sap, we can gain no information from his 

 labours ; as from the results of them we should 

 suppose that every different kind of tree must 

 have sap of a description peculiar to itself, which, 

 both the analogy of the animal kingdom, and the 

 knowledge we have of the nature of soils, inform 

 us cannot be the case. It is probable that the 

 water, the acetate of potash, and the carbonate of 

 lime, are taken up from the soil, and enter as general 

 constituents into the composition of sap ; but the 

 mucilage, the sugar, the extractive, the gallic acid, 

 the tannin, &c. are undoubtedly produced by the 

 vegetable system itself, and must, therefore, vary 

 in different plants. As we shall afterwards find 

 that all the productions of the vegetable system 

 can be resolved into carbon, hydrogen, and oxygen ; 

 each production' differing in its composition from 

 another in the proportion only of its components ; 

 it is easy to comprehend that, as from the water 



