The Conclufion. 3 6 j 
And fince we find fo great a quantity of 
air infpired and mixt with the fap , and 
wrought into the fubftance of vegetables , 
the advantage of ploughing and fallowing 
ground feems to arife not only from the 
killing the weeds, and making it more mel- 
low, for the fhooting of the roots of Corn ; 
but it is thereby alfo the better expofed to 
have the fertilizing, fulphureous, aereal and 
acid particles of the air mixt with it, which 
make land fruitful, as is evident from the 
fertility which the fword or furface of land 
acquires, by being long expofed to the air, 
without any culture or manure whatever.- 
We have feen many proofs of the great 
quantities of liquor imbibed and perfpired 
by plants, and the very fenfible influence 
which different ftates of the air had on their 
more or lefs free perfpiration : A main 
intention therefore to be attended to in 
the culture of them, is to take due care, 
that they be fown or planted in proper 
feafons and foils, fuch as will afford them 
their due proportion of nourilhment $ which 
foils, as they are exhaufled, muft, as 'tis well 
known, from time to time, be repleniflied 
with frefh compoft, fuch as is full of falincr 
falphu- 
