326 On the Food of Planis. 
scarcely any other dressing for their wheat. J well remem- 
ber, that in the parish of Lansamlet, in Glamorganshire, my 
father, who was very attentive to agriculture, put most of 
his stable dung on meadow Jand, and used only lime for 
wheat. He had two lime-kilns constantly burning for his 
own use, and with this manure he obtained the most abun- 
dant crops; but then his land was principally a dark vege~ 
table mould, and much of it was peat, which before it was 
drained had been a bog. On this land I have counted sixty 
grains to an ear, not picked and culled out of many. others 
as being longer than the rest, but taken by handsful at 
random. 
In his land, lime asa dressing was particularly apt, be- 
cause, as we know, it hastens the putrefactive process, and 
promotes the dissolution of vegetable substances, converting 
them quickly into vegetable mould. 
Now in my experiments there was no vegetable matter to 
be dissolved, and therefore no benefit, according to chemical 
principles, was to be expected from the lime. The trial was 
however made, and the received opinion as to the effect of 
lime is thus far confirmed. 
But in my experiments the lime appears to have been de- 
Icterious, This was not from its causticity, for the plants 
lived; but from its ction as a cement in forming a crust on 
the surface of the pots imper vious to air. For in these pots 
I remarked, that after rain the water stagnated, and did not 
readily penetrate as in the other pots. 
Free access of air to the roots of plants seems to be of 
vast*importance, and almost essential to their growth, With 
regard to seeds, access of air is absolutely needful to their 
vegetation. Hence it is that charlock ( Sinapis arvensis) will 
remain in the earth for centuries, if deposited below the ve- 
getating distance, as we have occasion to observe on Salis- 
bury plain, where no charlock is ever seen, unless when 
the downs are broken up. The land is then covered with 
it; but till then the seeds remain as 27 vacuo, and are there~ 
fore not liable to change. 
This deposit of seed must have happened i in most remote 
antiquity, 
