General Instructions. 



87. If roots of different things take different food out of 

 the same ground, how is it that the roots of an Oak tree, 

 or any other tree, destroy turnips or corn growing upon 

 the top of the ground in which the roots of the tree are ? 

 It is well known to gardeners, that to have flourishing 

 wall-trees you must not plant perennial flowers, or any 

 devouring plants, along the borders where they stand. 

 Mr. TuLL, during his arguments upon this subject, ob- 

 serves, that if plants of various sorts, fed upon nothing but 

 one particular portion of the soil, and left the rest for other 

 plants to feed upon, there could be very little reason for 

 keeping the ground clear from weeds; for that the weeds 

 being totally different in their nature from wheat, for in- 

 stance, might live very happily along with the wheat; that 

 they might reckon their seeds together in the same piece 

 of ground, without any injury to the crop of either ! This 

 absurdity was attempted to be got over by the adversaries 

 of Mr. TrjLL, by saying that the weeds robbed the wheat 

 of part of the air, that it would otherwise have had; that 

 they shaded it more or less, either at stem or at top. To 

 show the absurdity of this defence, which was, indeed, 

 nothing more than a miserable shuftle, Mr. Tull pro- 

 posed to leave a piece of wheat with a certain portion of 

 rather tall weeds in it ; to clear another piece of equal 

 extent of all weeds whatever; and then, to stick up 

 amongst the wheat which had been cleared of the weeds 

 little sticks or twigs, in bulk equal to the weeds in the other 

 piece of wheat ; and then he ventured to pledge his life, 

 that the crop in the piece of wheat having the weeds left 

 in it, would not amount to more than three -fourths of the 

 crops having the sticks and the twigs. None of his adver- 

 saries ever accepted the challenge, and his principles re- 

 mained triumphant. 



