INORGANIC CONSTITUENTS OF PLANTS. 171 



while, the coloring-matter will all be returned to the soil. 

 When, therefore, a plant has not a sufficient quantity of its 

 appropriate alkali, it will take up some other, but may return 

 it to the soil, when that alkali is supplied ; hence, the impor- 

 tance of supplying the appropriate alkalies and alkaline earths, 

 for the perfect development of every species of plants. 



The source of the inorganic constituents of plants, is a 

 point much more easy to determine, than the particular form 

 and mode of their introduction into the organs of plants, and 

 of their assimilation. 



1. Pgtassa. Whence do plants derive their potash? 

 This question is easily answered. The rocks contain large 

 quantities of potash, locked up in the feldspar. Granite rocks, 

 such as exist abundantly in New England, contain about 

 seven per cent, of potash, in the form of a silicate, that is, 

 united with silicic acid. This potash is eliminated by the 

 action of the air, and by carbonic acid ; but growing plants 

 possess the power of decomposing the rocks, and of obtaining 

 it in much larger quantities. This is proved by the fact, that 

 plants growing in a glass vessel, will decompose the glass, to 

 obtain the potash which enters into its composition. 



The quantity of potash in a soil, is sufficient to sustain 

 most plants for an indefinite period of time. We might al- 

 most say, that it is inexhaustible ; for pine plain soil 

 of six inches in depth, contains, per acre, thirty-six tons of 

 potash, and a ton and a half of lime. Some plants, however, 

 such as wheat and tobacco, by being planted upon the same 

 soil for a series of years, will exhaust the potash to such an 

 extent, that a change of crops must be resorted to, to restore 

 fertility. There may be some cases, in which minerals be- 



of blossom, is sprinkled with the juice of the Phytolaca decandra 

 (American nightshade), the white blossoms assume, in one or two 

 hours, a red color, which again disappears after a few days under the 

 influence of sunshine, and they become vv^hite and colorless as be- 

 fore," — L. 



