64 ^ OR CHANGE OF SPECIES. Parti. 



that the feeds muft partake of the weakly difpofition of the plant 

 which produced thenij and that their produdlions cannot be fo fine 

 as thofe which grow from the feeds of firong and healthy plants. 

 For this reafon Mr. Tull advifes to take the feed corn from a richer 

 foil than that in which it is to be fowed, and rather from well 

 cultivated land, than from land that is not fo. We cannot fay we 

 think him wrong ; tho' the contrary opinion is almofc generally 

 received : becaufe, the firfb produdtions of a fine good feed, being 

 flrong and well conditioned, more may reafonably be expedled 

 from them, than from a poor weakly plant. 



Another advantage in changing the feed, is, that there are fome 

 weeds which delight in particular fpots, and do not grow fo freely 

 elfewhere. If a farmer fows wheat of his own growth, he increafes 

 the weeds which thrive particularly in his land ; whereas, by 

 changing his wheat, the weeds which he brings into his ground, 

 not being in the foil that agrees belt with them, will do lefs da- 

 mage to his corn. 



However, Mr. Tull thinks, that change of feed may be dif- 

 penfed with, by the means of the new hufbandry ; becaufe, by his 

 method of culture, almoft all weeds are deftroyed, and the plants 

 being very ftrong, their feed ought to be preferred to any other for 

 fowing ; efpecially when they are not foreign plants, which borrow 

 their quality from the climate they are raifed in. 



What is here advanced may admit of fome difficulty, for it is 

 known, (and Mr. Tull allows it) that fmall wheat produces as ftrong 

 plants as the largeft. If fo, wheat that has grown in bad land, 

 would be as good for fowing as the very fineft, provided it were 

 well conditioned in other refpecls. 



Dr. Home, p. 136. accounts very rationally for the advantages 

 .arifing from changes of crops, from the different effects of their roots. 

 " The- fibrous rooted divide direftly into fmall fibres which run in all 

 " diredlions, but mofily horizontally. The carrot-rooted fend one 

 *' great ftem directly down, which has lateral fibres. The former, 

 *' in which clafs are reckoned all the white grains, rye grafs, &c. 

 " confolidate the ground ; while the latter, in which clafs are rec- 

 *' koned the leguminous plants, turneps, carrots, clover, attenuate 

 ** and loofen the earth exceedingly. The fibrous roots muft bind 

 " the foil together like fo many threads, while the carrot-roots 

 *< divide like a wedge, and by their mere mechanical force, cut the 

 " earth. The leguminous plants, by covering the foil, keep it 

 I moift. 



