98 CHYMISTRY APPLIED TO AGRICULTURE. 



salts ; so that those plants, and those portions of the same^ 

 plant, which transpire most, must necessarily contain the 

 greatest quantity of salts. 



The salts and earths contained in plants are of the 

 same nature as those existing in the soil in which they 

 grow, but not, according to analysis, in the same propor- 

 tions; because the plant absorbs more or less of them ac- 

 cording to its own nature and their solubility. It cannot, 

 however, be strictly said, that all the salts contained in 

 plants existed previously in the soil, as some neutral salts 

 are evidently formed within their organs ; such are those 

 of which the acid is known to us, and particularly those 

 that contain in their composition a vegetable principle : of 

 this sort are the acetates, the malates, and the citrates. 

 The salts do not exist after the burning of the plant, be- 

 cause their acid is decomposed by the action of fire, and 

 there remains only their base, which is usually potash or 

 lime ; but an analysis of the plant " by the wet way " gives 

 proof of their existence. 



It is even possible in some cases to follow the formation 

 of the acid, by observing the progress of vegetation, and 

 the changes produced in its products. Of this I will men- 

 tion one example. Beets gathered late in autumn, in the 

 north of France, do not yield the same principles as those 

 gathered at the same period in the south of France ; the 

 first contain sugar, the second salt-petre. According to 

 the experiments carefully made by M. Darracq in the de- 

 partment of Landes, the beet roots of the south yield as 

 much sugar in the month of August and the earlier part 

 of September, as those of the north ; this sugar then is 

 replaced by salt-petre, of which the acid is formed during 

 the progress of vegetation. It has been observed, that 

 beets containing sugar frequently underwent a change 

 during the winter, by which the sugar entirely disappeared, 

 and was replaced by salt-petre ; in this case we can almost 

 follow with the eye the process of decomposition. The 

 juice of beets in which the change has commenced, when 

 thrown into the boilers, becomes covered with a thick, 

 white foam, which gives out a reddish vapor of nitrous 

 gas: in this state the labor of extracting sugar becomes 

 very difficult ; the sugar crystallizes badly, and the propor- 

 tion of molasses is very great. It may be seen clearly, that 

 in this state oxygen is already united in the beets with 

 azote, and that only an additional portion, which would be 



