392 On the Continuous Growth of Wheat on the 
prosperity, while the second period has witnessed a more severe 
depression than any that has occurred during the present 
century. 
An attempt to investigate the growth of wheat under circum- 
stances so totally different from any which have ever previously 
arisen, could hardly be carried out without the commission 
of some errors which experience would have enabled us to 
avoid. We now know — if we wish to advance beyond the 
question of the best manure to grow one crop of wheat — that 
continuity of manuring is of supreme importance. With the 
exception of the plot receiving farmyard dung, and the un- 
manured plot — neither of which has been altered from the 
commencement — there is no plot in the field in which some 
change has not taken place in the manure applied during the 
early years of the experiment. But in 1851, 7 years after 
the experiments were commenced, the manuring of the field 
was arranged upon a fixed plan which — with very slight 
changes in one or two instances — has been continued up to 
the present time. 
Upon the plot receiving farmyard dung, and the unmanured 
land, no change has taken place during the 40 years ; upon most 
of the other plots, which comprise about 16 experiments, no 
change has taken place for 32 years. 
In our former paper we devoted some time and space to 
the purpose of considering, and refuting the views held by 
Baron Liebig with respect to the growth of wheat. All con- 
troversy in regard to these once celebrated theories has died 
out. There is no question at the present time regarding the in- 
gredients in which soils cropped repeatedly with corn are gene- 
rally deficient ; nor is there any question as to what substances 
must be applied with a view to increasing the produce. A 
possession of this knowledge enables us to forecast with some 
degree of certainty — subject of course to the influence of climate 
— what will be the relative yield of the various manures applied 
to our experimental crops, for some considerable period in 
advance. 
Coincident with an increase of knowledge in this direction a 
completely new branch of enquiry has sprung up. 
Analysis tells us that a very considerable proportion of the 
ingredients we apply to grow the crop is not found in the 
produce. What has become of this proportion ? 
Again, the greater part of the crop consists of ingredients 
which are not supplied. What is the source of these in- 
gredients ? 
The carbon, which is the source of heat in our fires, is taken 
out of the soil in the form of coal. If we increase the carbon 
