572 PROCEEDINGS OF SECTION G. 
large extent ignorant of the state of a soil at any given 
moment; and this ignorance, from the nature of the case, 
we are hardly likely ever to dispel, although research will 
almost certainly enable us to reduce it very considerably. 
As a large proportion of the constituents of a soil are either 
potential plant-foods—that is to say, substances which, 
although unable in their present condition to feed plants, 
are capable of being changed into forms which plants can 
take in and assimilate—or are useful as well in other 
respects, because they perform functions by means of which 
they contribute indirectly to the formation of assimilable 
plant-foods, this state of chemical unrest or instability in 
the soil is the means by which it is kept supplied with 
assimilable plant-foods. The more compiex, in fact, a soil 
is in its constitution, and the more exposed to forces which 
disturb its chemical equilibrium, and the greater the 
activity of these forces, the greater, ceteris paribus, is its 
capacity for feeding plants likely to be. Nor are the 
activities in a soil chemical alone. It is the theatre of other 
activities as well. It contains living organisms; and the 
bacteria with which it often teems, and can be made to 
teem, contribute largely to the formation of assimilable 
piant-foods in it—directly by the production of assimilable 
nitrogenous food; and less directly by helping to break up 
organic substances into other substances which cause 
chemical changes in it. 
The agricultural progress I have in view in the title of 
this paper, is the making of such improvements in our 
methods of tilling and managing the soil as will enable us 
to increase, and, if possible, give direction to the activity 
of the chemical and biological (bacterial) forces which are 
incessantly at work in it, and cause them to change potential 
plant-foods into available forms in greater abundance than 
they do by means of our present methods. I do not venture 
to predict how much progress can be made in this direction ; 
but it seems to me that as comparatively little effort of a 
systematic character, so far as I know, has been made in 
the field with this object in view, and that as the soil is 
known to be in general well supplied with potential plant- 
foods—sometimes within eight inches of the surface with 
enough for some hundreds of crops—it would be a far more 
philosophical course to make it our aim to learn how to 
make the greatest possible use of these potential plant- 
foods, than to devote our energies almost exclusively, as 
until lately we have been doing in our field-experiments, to 
the study of hand-feeding our crops with manures. I do 
