760 DISCUSSION ON WHEAT: 
(4) Continuous Wueat Growine.—At Rothamsted, where wheat 
has been growing on the same land for more than sixty years, there is 
little evidence of any secular decline in the yield due to the constant repeti- 
tion of the crop, provided that sufficient fertilisers are supplied. On the 
unmanured plot and in cases in which complete fertilisers are given, the 
production tends to reach a constant level when -long-period averages are 
taken to exclude the fluctuations due to season. That the Rothamsted yields 
are never so high as are sometimes attained under ordinary farming con- 
ditions is due to the type of soil and certain difficulties in cleaning and 
preparing the land when wheat follows wheat so rapidly. 
(5) It is not, however, possible to analyse completely all the factors in- 
volved. Type of soil in relation to climate is very important. Thus the 
Rothamsted plots, even those receiving abnormally large dressings of 
manure, have only on two occasions (1864 and 1894) approached 50 bushels, 
which on a good brick earth would be by no means an exceptional crop even 
when grown, as usual in England, with but little manure. To each type of 
soil there is a limiting yield beyond which the crop will not go. But the 
limit is not the same for all varieties; it is not unusual to find that one 
variety may do much better than another under one set of conditions but 
not so well under others. There is still a good deal of work to be done in 
inquiring into the soil conditions and reducing to precise terms such vague 
expressions as ‘ a good wheat soil.’ For example, on soils not very dissimilar, 
with the same rainfall and management, a heavy wheat crop will stand in 
one case, while on the other soil it will invariably go down, and as yet it is 
impossible to state definitely the factors which thus determine the stiffness 
of straw in one case and not in another. As wheat is largely a pioneer crop, 
and as the pioneer cannot control his conditions to anything like the extent 
that is possible in more developed parts of the country, it is important that 
wheat should be bred to suit local conditions. 
3. The Breeding of Wheat. By Professor R. H. Birrmn, M.A. 
The widespread cultivation of wheat from very early times has led 
directly to the production of a very large number of distinct varieties, 
so that growers have abundant opportunity of choosing those which best 
suit their special conditions of cultivation. Wide as the choice is, however, 
few will care to admit that they have precisely the varieties they could 
wish for at their disposal; the improvement of existent types is, in fact, 
demanded in practically all directions. In most parts of the world the 
features of outstanding importance are strength, resistance against disease, 
and yield. Under certain conditions the power of resisting drought and 
that of maturing early are also of extreme importance, and any improvements 
in these directions would lead at once to a great increase in the area within 
which the crop can be cultivated. 
Most of the wheat-growing countries recognise these facts, and several 
have made considerable efforts either to find wheats suitable for their needs 
or in some cases to produce them by cross-breeding. In Australia, Canada 
and the United States such wheat-breeding experiments have been in 
progress during the past twenty years. On the whole the experiments 
cannot yet be said to have met with the success they deserve, with the 
possible exception of Farrer’s in Western Australia, which promise to effect 
radical alterations in the types of wheat cultivated there. The reasons for 
this partial failure are now obvious. Breeders had no definite knowledge 
of the results to be expected from any particular cross. They knew in a 
general fashion that the operation resulted in ‘breaking the type’ or 
inducing ‘great variability,’ and there was always a hope that amongst the 
