Observations on Manures , 337 
chicory cichorium intubus ) would be luxuriant where no other 
grass would grow. 
III. I come now to consider the mode of accelerating the growth 
and increasing the size of plants. 
This is done by manures , Hitherto, every substance added to 
soil or to the plant while growing, which effected, or was meant 
to effect these purposes, was called a manure. But, from what has 
been said, manure ought to be considered in at least four divisions. 
1. Manures of nourishment. 2. Manures of stimulus. 3. Ma- 
nures of moisture. 4. Mechanical manures. 
Manures of nourishments Five different theories have been 
started on this subject, the pabulum of vegetables. 
1. Practical men have for ages discovered the use of dung in 
agriculture, and hence the common and oldest theory was, that the 
juices of decomposed animal and vegetable substances in the gross, 
were the chief pabulum of plants. 
2. Vanhelmont’s experiment suggested water as the pabu- 
lum, but although some plants will live, none will flourish in mere 
water.. ..The French experiment of the decomposition of water, 
and the discovery of the excretion of oxygen, give countenance to 
the opinion that water, though not the pabulum, is decomposea- 
ble, and is a pabulum ; furnishing hydrogen : and it is also a com- 
ponent part of the plant even as water. The curious experiments 
of M. Braconnot add strength to this opinion. It is not yet known 
whether plants can decompose azot, but I am strongly inclined to 
suspect this substance to be a compound, for we have no fact to 
shew that animals absorb it from the atmosphere. 
3. Dr. H un ter, of York, in his Georgical Essays , persuaded 
the world for some time, that oil was the pabulum of vegetables. 
But neither his theory nor his practice succeeded. 
4. Dr. Priestley, who had more right to form theories and 
conjectures than any man living, (because he furnished more 
facts of extensive application in chemical philosophy than any 
other man,) suggested that phlogiston was the pabulum. Some 
experiments of Arthur Young, made in consequence of this 
supposition, tend to support it. But though in all probability in - 
fammable gas may be converted into nutriment to vegetables, yet 
it is far from being true, that this is the only gas which can. The 
gasses that escape from a dung-hill contain much carbon, azot, and 
ammonia, as well as various stimulating saline compounds. We 
know too, that electricity, and the galvanic fluid, seem to aid v,e- 
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