1 8 Of Food of Plants. Chap. II. 



to it ; and then no more of thefe Grains will grow in 

 that Land, till by Fallow, Dung, and Influences of 

 the Heavens, the Earth will be again repleninYd with 

 new Nouri foment, to fupply the fame Sorts of Corn 

 over again. This, if true (as they all affirm it to 

 be), would prove, that the Air is not the Food of Ve- 

 getables. For the Air being in itfelf fo homogene- 

 ous as it is, coukl never afford fuch different Matter 

 as they imagine ; neither is it probable, that the Air 

 mould afford the Wheat Nourifnment more one 

 Year, than the enfuing Year ; or that the fame Year 

 it fhouid nourifh Barley in one Field, Wheat in an- 

 other, Peafe in a Third -, but that if Barley were fown 

 in the Third, Wheat in the Firft, Peafe in the Se- 

 cond, all would fail : Therefore this Hypothefis of 

 Air for Food interferes with, and contradicts this 

 Doctrine of Neceftity of changing Sorts. 



I fuppofe, by Air, they do not mean dry Particles 

 of Earth, and the Effluvia which float in the Air: The 

 Quantity of thefe is too fmall to augment Vegetables 

 to that Bulk they arrive at. By that way of fpeak- 

 ing they might more truly affirm this of Water, be- 

 caufe it muff be like to carry a greater Quantity of 

 Earth than Air doth, in proportion to the Difference 

 of their different fpecific Weight 5 Water, being about 

 800 times heavier than Air, is likely to have 8co 

 times more of that terreflrial Matter in it; and we fee 

 this is fufficient to maintain fome Sort of Vegetables, 

 as Aquatics ; but the Air, by its Charge of Effluvia, 

 &c. is never able to maintain or nouriifi any Plant •, 

 for as to the Sedums, Aloes, and all others, that are 

 fuppoled to grow fufpended in the Air, 'tis a mere Fal- 

 lacy 5 they feem to grow, but do not ; fince they con- 

 ftantly grow lighter; and tho' their Veffels may be 

 fomewhat diflended by the Ferment of their own 

 Juices which they received in theEarth, yet fufpended 

 in Air, they continually diminiffi in Weight (which 

 is the true Argument of a Plant} until they grow to 



nothing, 



