144 
Superphosphate of Lime. 
some results in corroboration, yet I do not hold them as es- 
sential to the subject, so fully has the success of the mixture been 
established by the numerous experiments related in the Journal 
of the Royal Agricultural Society, and more particularly in the 
excellent and elaborate Essays of Mr. Hannam. And though I 
shall find it necessary to pass rapidly over all the various branches 
of the subject, yet my claims for honorary notice will principally 
rest on affording: such practical information on points hitherto but 
briefly attended to, as may, I hope, render this Essay of really 
practical and pecuniary value to agriculturists in general. 
The specific effect of bone as food for the turnip-crop has 
long been known — long mdeed before Science was in a position 
to explain the cause of its peculiar effects, or to assign correctly 
to what portion of its constituents the benefits are chiefly due. 
It was found, greatly to the surprise of many, that burnt bones, 
in which of course the organic parts had been destroyed, were 
equal if not superior in their effect to bones not so treated ; and 
that when boiled, in which state the fat had been expelled, they 
were more productive than bones in a fresh state. It was thence 
supposed by those who jumped to conclusions too hastily, that 
the substances thus expelled were useless at any rate for the 
turnip crop, and they were apparently supported by the theory 
of a very eminent chemist, who, if we mistake not, laid it down as 
his opinion that the value of manures depended principally if not 
entirely on their inorganic ingredients — a doctrine altogether at 
variance with the previous generally received notions, that am- 
monia was the true fertilizing element, and that its amount 
afforded the measure of the value of manure. Inmedio tutissimus 
ibis — the truth, we take it, will be found to lie between the two 
extremes. We may justly regard the inorganic constituents as 
being the most important and essential portion of manure, af- 
fording to the plant what the skeleton does to the animal, the 
basis of support ; and as plants can obtain no other supply but 
through the soil, we may justly regard them as the most essential 
constituents. 
The other elements are to a great extent supplied through the 
atmosphere, and even nitrogen and its combinations may be thus 
furnished. The avenues through which this atmospheric supply 
is furnished are the leaves of the j)lant, and their size afford a 
correct criterion, cceteris paribus, of the amount of nutriment de- 
rived from the aerial source. Thus beans and other pulse obtain 
more food from the atmosphere than cereal plants ; roots more 
than the former; and wheat, from the small size of the leaves, less 
tlian any. Thus only can we account lor the striking fact that if 
we give a good supply of inorganic elements only to the turnip- 
crop, we shall very probably have a plentiful crop, whilst if these 
