LECT. III.] THE SAP. 115 



of plants as consisting of water which is its prin- 

 cipal component, carbonaceous mattery acetate of 

 potash, and carbonate of lime*; which ingredients 

 are decomposed by the vital powers of plants, and 

 new combinations of their constituents produced 

 by the same powers, so as to form the different 

 parts of which a plant consists. The large portion 

 of vegetable matter contained in the first sap, as 

 we have already noticed, must have been previ- 

 ously deposited in the cells of the root, and taken 

 up by the water of the sap in its progress upwards : 

 and air which is also found in sap, as Mr. Knight 

 has demonstrated, is either the produce of vege- 

 tation, or is taken in by the roots dissolved in the 

 water of the soil-f~. 



Such is the nature of the sap. In spring and at 

 midsummer it forms a large portion of the vegetable 

 body ; and is carried forwards through the vessels, 

 with an impetus sufficient to raise it to the summits 

 of the highest trees, until arriving at the leaves, in 



* The enumeration of these ingredients as the general com- 

 ponents of sap, cannot be objected to because many other 

 saline and earthy matters are occasionally found in sap ; those 

 depending altogether on local circumstances affecting the soil. 



f Sir H. Davy, in his Lectures on Agriculture, has adopted 

 the opinion of Feburier, that the sap is found in two states ; one 

 kind in the vessels of the alburnum, containing chiefly saccha- 

 rine matter, mucus and albuminous matter, and another in the 

 bark, containing tannin and extract ; but I am not inclined to 

 regard any juice found in the bark as ascending sap ; and) there- 

 fore, cannot subscribe to this opinion. 



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