232 
The Present State of Agriculture 
c. Intiinatoly connected with this inquiry is the important one 
as to the state in which it is the most profitable or economical to 
apply this or that substance to the soil, so as in the greatest degree 
oxalic acid as above explained. More time consequently would be de- 
manded, and growth we should expect would be less rapid on this sup- 
position than it' the required radical were produced or prepared by some 
other agency, or were obtained directly from the root. 
Suppose that the ascending sap brings up towards the leaf substances 
poor in oxygen, and we have a portion of the work already performed, and 
the growth of the plant may in consequence be more rapid. 
Now the organic matter of the soil is characterised by the presence of 
rather less oxygen in proportion to its carbon and hydrogen than is con- 
tained in the recent substance of plants; and the processes of fermentation, 
&c. by which manures are prepared in the farm-yard are all so many 
methods by which the proportion of oxygen contained in its vegetable 
matter is lessened. 
This is all in favour of the view that the soil and root contribute to the 
growth of plants by lessening the labour of the leaves,— by providing sub- 
stances which contain less oxygen to combine with those which enter by 
the leaf and contain much. Could we not, therefore, aid the growth fur- 
ther by feeding the roots with substances which contain no oxygen at all ? 
Ammonia which contains none is much used, and with advantage, though 
the principal part of its useful action is generally ascribed to the nitrogen 
it contains. 
But in those parts of India where petroleum wells abound, this substance 
is said to be used as a manure for the date tree, and among ourselves coal 
tar has been applied with advantage to our common crops. Is it unreason- 
able, therefore, to suppose that turpentine and naphtha-like substances may 
be employed profitably as manures i" A trial of them is suggested by the 
above theory ; and should such trials lead to no profitable result, yet other 
trials suggested by such views may, and thus practical agriculture will ap- 
pear to be promoted by the most refined speculations of the laboratory and 
closet. 
The reader will perceive that the very idea of such things as I have 
mentioned being useful to plants, is entirely opposed to the view which 
ascribes to the organic matter of the soil the function of supplying carbonic 
acid only to the roots of plants. But supposing we received such a view 
as the most consistent with our present knowledge, which I do not think 
it is, this should not prevent us from following up any new idea, or from 
giving a fair experimental trial to the suggestions to which new theoretical 
views may give lise. 
We do not understand very well as yet how whale oil and whale blubber, 
and other fatty matteis, form good manures, and yet some of our Lincoln- 
shire friends find the purchase of oil for the manufacture of composts for 
their turnip-crops a source of profit. May not the use of oil, of petroleum 
and of coal tar all find their explanation in some theoretical view similar 
to that stated in this note, and does this view not fairly suggest the pro- 
priety of further trials with similar substances ? 
I give the above, the reader will remember, not as a statement of opinion, 
but as an illustration only of the way in which theoretical views and re- 
searches connect themselves with the profitable practice and with the ex- 
tension of the agricultural art. I might have adduced an easier and 
simpler one, but I have purposely selected a theoretical speculation, 
which at first sight appears as far removed as jjossible from anything like 
a practical application to agriculture. 
