352 
Chemical Composition and Commercial Value of 
men, gluten, legumine, and indeed all albuminous compounds. 
How large then is tlie demand for those constituents which even 
the best soils supply but in scanty proportions I We can thus 
understand why their direct supply in an available condition is 
of more vital importance to our cultivated crops than that of 
any other fertilizing substance. 
Generally speaking, phosphatic manures produce a more 
marked effect upon root-crops than upon cereals. At one time 
it was supposed that root-crops removed more phosphoric acid 
from the soil than white crops, and on that account required to 
be more abundantly supplied with phosphates. But this expla- 
nation is as little correct as all others in which no account is 
taken of the respective periods of vegetation of green and white 
crops, and the different mode in which these crops take up the 
food at their command in the soil. The roots of swedes and 
turnips, unlike the deep penetrating roots of the wheat-plant, 
with their numerous fibriles, feed, comparatively speaking, upon 
a small portion of the cultivated soil, and their whole period of 
vegetation is very much shorter than that of our cereals, espe- 
cially that of wheat. Whilst the wheat-plant is thus enabled 
to search for proper food in a consideral)le depth of soil, and 
by degrees accumulates in its organism the requisite amount of 
phosphoric acid which is distributed in small quantities in a 
large mass of soil, turnips, swedes, and mangolds, in consequence 
of the peculiarities of their growth, do not find at their disposal 
available phosphoric acid in sufficient quantity to supply that 
weight of bulbs which we now look for in average seasons. 
Hence it is that manures, rich in soluble phosphates, produce 
such a striking effect on root-crops, no matter what the character 
of the soil may be on which they are grown. 
Although superphosphate and bone-dust do not generally 
benefit wheat to the same extent as turnips, these and other 
phosphatic manures are very efficacious when cereals are grown 
on light sandy soils or land naturally very poor in phosphoric 
acid. I do not purpose to institute at present a minute inquiry 
into the relative utility of the various organic and mineral con- 
stituents which constitute the food of plants, nor to extend the 
preceding observations. They are merely offered as suggestions 
which to some extent, at least, explain the fact that the sale of 
phosphatic manures has been steadily increasing from year to 
year, and has now assumed gigantic dimensions. 
The supply of bones is totally inadequate to meet the present 
large demand for superphosphate and sijnilar fertilizers. It is 
fortunate, therefore, that England possesses an abundant source 
of phosphates in the extensive Suffolk and Cambridgeshire 
coprolite deposits, and that the enterprising character of English- 
