The Conchjion. 3 6$ 
thofe which grew in different foils* and were 
any how cultivated in a different manner 
from each other 5 this would inform them 
alfo* whether they fowed their Corn too 
thicker too thin* by comparing the branch- 
ings and extent of each root* with the fpace 
of ground allotted it to grow in. 
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* aerealand 
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 fates of the air had on their 
more or lefs free perfpiration : A main in- 
tention therefore to be attended to in the 
culture of them* is to take due care* that 
they 
