Chap. IV. OF THE FOOD OF PLANTS. 5 



part of that food, feeing that plants become earth by putrefadion j 

 and the other principles ferve, perhaps, only to render earth fit for 

 the nourilliment of plants. 



Salt, for example, may attenuate earth, water may enlarge its 

 particles, and air and fire give it a due motion and adlivity : but 

 earth feems to be the effential part. The plant would indeed die, 

 if deprived of the other elements : but without earth, not even a 

 fkeleton of it would remain. 



The earth we are fpeaking of, is not a fimple elementary earth, 

 or caput mortmwi, but that compound fubllance called mould ; for 

 all the principles we have mentioned, may be extracfted from the 

 dead plants.. It may hence be admitted, that earth is the principal 

 food of plants : efpecially as it is known, that too great a quantity 

 of fait renders earth barren, too much water drowns and rots plants, 

 too much air dries up their roots, if expofed to it, and too much 

 heat (or fire) burns them. But plants are not hurt by too much 

 earth : for if a plant languiilies \^'hen its roots are buried too deep, 

 it ought not to be imputed to the quantity of earth that covers 

 thofe roots, but to its not enjoying the moiflure of the dew, the 

 warmth of the fun, the influences of the air, Oft". 



But it is not the defign of a Treatifc of Agriculture, to enter into 

 the difcufiion of fo difiicult a queflion as what is the real food of 

 plants. We fliall therefore, with Mr. Tull, confider earth greatly 

 attenuated, as the immediate food of plants, without deciding whe- 

 ther it be fimple, elementary, and void of all other fubftance. 



Of whatever nature the fubllance which nourifhes plants may 

 be, we ihall examine in the jiext chapter whether it be nearly the 

 fame for difi^erent kinds of plants. 



CHAP. IV. 



Whether the moji different kinds of Plants draw the fh?ne fort of 

 fubj}ance from the earth, for their Food. 



IT is generally thought that each difi-'erent fpecies of plants is fed 

 by different juices. The chief arguments for and againil tliis 

 opinion, are as follow : 



I. It does not feem probable, fay thofe who are for- it, that the 

 fame homogeneous matter can be the food of fo many plants, v/hich 

 differ fo widely from each other in their fiiape, colour, tafte, and 

 properties. 



To 



