244 THE FLUID COMPONENTS OP PLANTS. 



taining a perfect knowledge of this part of the vegeta- 

 ble economy ; for to obtain such a knowledge of the 

 nature of sap would require an examination of that 

 fluid in a greater number of different species of plants, 

 than the opportunities, and the period of any life, 

 would permit. All that we can aim at, therefore, in 

 the present state of our knowledge, is the formation of 

 a probable hypothesis, rather than the attainment of 

 truth deduced from certain experiments. In this 

 mode of viewing the subject, we may regard the sap 

 of plants as consisting of water which is its principal 

 component, carbonaceous matter, 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, must have been previously 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, is either the produce of vegetation, or is taken 

 in by the roots dissolved in the water of the soil. 



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

 midsummer it forms a large portion of the vegetable 

 body ; and is carried forward through the vessels, 

 with an impetus sufficient to raise it to the summits of 

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

 it is exposed to the action of the air and light, the 

 great quantity of water it contains, being no longer ne- 

 cessary, is thrown off by perspiration; whilst the suc- 

 cus proprias, or peculiar juice of the plant, from which 

 all its secretions are formed, is produced by the 

 changes resulting chiefly from this exposure. We 

 have, therefore, next to proceed to examine the na- 

 ture of this peculiar juice, as one of the general com- 

 ponents of plants. 



