FOOD OF PLANTS. 1<J3 



in the soil, torrcdier with what is derived from the fitrnosphere, 

 more than compensates tor the stalk, wliieh is taken away ; 

 that is, ll»e si»il has received more vegetable food iVom llie at- 

 mosphere and the roots, than it lias yielded to man. Jiut 

 Boussingauit takes a more extensive view of the subject. He 

 supposes a farm devoted to the cultivation of grain, possessing 

 of course, a sulhcient amount of stock; one knows by expe- 

 rience what quanlity of manure is indispensable, therefore the 

 relation which ought to exist between the surface cultivated 

 in tcrage, and that devoted to the cultivaiion of merchantable 

 'duce. Fach year they will export grain, cheese, and some 

 inals. Tiius there will be a constant export of azotic pro- 

 ducts, without any importation of similar mutter, and during 

 all this time the fertility of the soil is not impaired. The or- 

 ganic material constantly exported, will be replaced by the 

 culture of ameliorating j)lants or by fallowing ; and the art of 

 agriculture consists in adopting the rotation which best favors 

 the most prompt transition of the elements of the atmosphere 

 into the soil. 



173. The above is a true representation of the course pur- 

 sued on numerous farms, where there is a constant exporta- 

 tion of products, but no importation of manure, and yet the 

 farms are increasing in richness ; but we are sorry to remark 

 tluit the s )il of many other fariis within our acquaintance 

 kvhich export o more, by carelessness and mismanagement, is 

 bccomin^j exhausted. The latter class of farmers are inflict- 



' serious injury on posterity, as it will require a long series 

 .. \ears to bring back an exhausted plantation to a slate of 

 fertility, although it requires but little proper management to 

 keep a good plantation good for ages. 



174. But besides the above named eleu:cnts, various othVr 

 substances enter into the composition of vegetable food, which 

 act in hardening the tissue, and some of them pro'jiibly as 

 stimulants to the vegetable functions. Some plants require the 

 presence of siiex in order to form their appropriate tissues, as 

 the cane, corn and grains generally. The various salts of lime 

 enter into the composition of vegetables, as the j)hosph.itc in 

 the Phytolacca, the oxalate in the Iris and Rhubarb. Potash 

 enters into the composition of all plants not exposed to the 

 ion of salt water, and those that are thus exposed, con- 



j soda. From the ashes of the former, the potash, 

 and from those of the latter the soda, of commerce, are ob- 

 tained. 



175. From this constitution of vegetable.*, different plants 

 require different soils for their production in the highest de- 



12 



