ON THE CHEMICAL CONSTITUENTS OF SOILS. 209 



A similar cause forces corn-plants to extract silicic 

 acid from the soil. The number of acids found 

 in different plants is very numerous, but the most 

 common are those which we have already mentioned; 

 to which may be added acetic, malic, citric, aconitic, 

 maleic, kinovic acids, &c. 



When we observe that the proper acids of each 

 family of plants are never absent from it, we must 

 admit that the plants belonging to that family could 

 not attain perfection, if the generation of their 

 peculiar acids were prevented. Hence, if the pro- 

 duction of tartaric acid in the vine were rendered 

 impossible, it could not produce grapes, or in other 

 words, would not fructify. Now the generation of 

 organic acids is prevented in the vine, and, indeed, 

 in all plants which yield nourisliment to men and 

 animals, when alkalies are absent from the soil in 

 which they grow. The organic acids in plants are 

 very rarely found in a free state ; in general, they 

 are in combination with potash, soda, lime, or mag- 

 nesia. Thus, silicic acid is found as silicate of 

 potash, acetic acid as acetate of potash or soda, 

 oxalic acid as oxalate of potash, soda, or lime, tar- 

 taric acid as bitartrate of potash, &c. The potash, 

 soda, lime, and magnesia in these plants are, there- 

 fore, as indispensable for their existence as the 

 carbon from which their organic acids are produced. 



In order not to form an erroneous conclusion re- 

 garding the processes of vegetable nutrition, it must 

 be admitted that plants require certain salts for the 

 sustenance of their vital functions, the acids of 

 which salts exist either in the soil (such as silicic or 

 phosphoric acids) or are generated from nutriment 

 derived from the atmosphere. Hence, if these salts 

 are not contained in the soil, or if the bases neces- 

 sary for their production be absent, they cannot be 

 formed; or in other words, plants cannot grow in 

 such a soil. The juice, fruit, and leaves of a plant 

 cannot attain maturity, if the constituents necessary 

 for their formation are wanting, and salts must be 



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