48 VEGETATION. 



constituting a small proportion of vegetable food, they 

 are not of themselves sufficient to support the plant, 

 even with the assistance of water. Giobert mixed to- 

 gether the different earths in such proportions as are 

 generally to be met with in fertile soils, and moistened 

 them with water. Several different grains were then 

 sown in this artificial soil, which germinated indeed, 

 but did not thrive ; and perished when the nourish- 

 ment of the cotyledons was exhausted. It is plain, 

 therefore, that the earths, though beneficial to the 

 growth of some vegetables, and perhaps necessary to 

 the health of others, are by no means capable of afford- 

 ing any considerable degree of nourishment to the 

 plant. 



6. MANURES. — As the object of the preceding pa- 

 ges, has been that of exhibiting a brief view of the dif- 

 ferent species of vegetable food, whether it be regard- 

 ed as derived from the soil or the atmosphere ; so our 

 next object will be to show how the food necessary to 

 the support of the vegetating plant may be supplied 

 when- defective, or restored when exhausted. But 

 this unavoidably involves the subject of manures, or 

 artificial preparations of vegetable food, so important 

 to the advancement of agriculture, and consequent in- 

 terest of mankind. 



With regard to the food of plants derived from the 

 atmosphere, the supply is pretty regular, for the pro- 

 portion of its elements is not found to vary on any part 

 of the surface of the globe, and if human aid were even 

 wanted, it does not appear that it could be of much 

 avail. But this is by no means the case with regard to 

 soils, which are less regular in their composition, and 

 at the same time, more within the reach of human 

 management. On this subject however, we can only 



