258 SECTIONAL ADDRESSES. 
the practical significance of the work lies in the fact that it greatly simplifies 
the agricultural problem hy providing plants more or less suitable to the 
existing natural conditions where otherwise the expert would have the 
difficult, if not impossible, task of making the conditions suit the available 
plants. The work has proved extraordinarily fruitful and has given 
astonishing results even in our own time. It has played no small part in 
the amazing development of wheat growing in Canada. When the British 
Association went to Winnipeg in 1909 we were all impressed by the fact 
that Canada had then passed the 160-million bushel mark in production, 
but who would have thought that within fourteen years the production 
would exceed 474 million bushels? Even in England, where wheat has 
been grown for 2,000 years, and where farmers have a long traditional 
knowledge of the crop, the new varieties introduced hy Biffen have increased 
the yields and the certainty of yields. The triumphs of Webber and others 
in the United States, of Nielson Ehle with cereals in Sweden, Jeffreys 
in standardising the quality of cotton in Egypt, the Howards in producing 
wheats for India, to mention only a few, are still fresh in our minds. In 
the first period in the development of agricultural science the honours 
in the matter of practical applications lay with the chemists for the artificial 
manures, but in the present period we must admit that they le with the 
plant breeders and selectors who, indeed, are only on the threshold of what 
they may yet accomplish. And this great practical purpose of finding 
or producing varieties of crops specially suited to local conditions would 
be further advanced if the work were done in co-operation with plant 
physiologists who could precisely define the modifications required. Much 
saving of time and effort could be effected if it were possible to set up some 
International garden where small quantities of the plant-breeders’ produc- 
tions could be grown, including those which each one has rejected as being 
unsuitable to his particular requirements. Many of these unwanted out- 
casts might prove of value in other conditions. 
A second generalisation is that the soil is not a fixed, constant thing, 
but is pulsating with change. It contains a great population of micro- 
organisms which, among otheractivities, decompose the dead plantresidues, 
producing nitrates, humic and other substances of great importance in crop 
production. But the numbers of these organisms fluctuate continually, 
and the bacteria at least change hourly ; the nitrates suffer equally rapid 
changes in amount. Even the mineral part of the soil is not constant in 
composition. Modern research work shows that many of the properties 
determining fertility in soils are due to the soil colloids, and some of the 
most important are attributable to calcium complexes.. These are unstable 
and are affected by the soil water. If the water is free from salts but 
contains carbon dioxide, the calcium may be replaced by hydrogen, and 
an acid soil results; if the water contains sodium chloride, the calcium is 
replaceable by sodium and the resulting complex may readily give rise to 
an alkalisoil. So far as is known, the changes are governed by the ordinary 
stoichiometric laws, the equilibrium following the usual course expected 
when a colloid is concerned. But the important fact emerges that any 
soil not well supplied with calcium contains within itself the possibility of 
becoming acid and therefore infertile, or alkaline and probably sterile, 
according to the nature of the soil water soaking through it. The various 
biological and chemical changes tend to alter the composition of the soil 
