760 TRANSACTIONS OF SECTION M. 
the allied subject of variety testing, which has been brought into great pro- 
minence recently by the introduction of new varieties of many kinds of farm crops. 
In testing a new variety it is necessary to measure two properties—its quality 
and its yielding capacity—for money-return per acre is obviously determined by 
the product of yielding capacity and quality as expressed by market price. 
I propose here to deal only with the determination of yielding capacity. The 
determination of quality is not allied to manurial trials. 
In attempting to determine yielding capacity there has always been a strong 
_ temptation to rely on the measurement of obvious structural characters. For 
instance, in the case of cereals many farmers like large ears, no doubt with the 
idea that they are an indication of high yielding capacity. Many very elaborate 
series of selections have been carried out, on the assumption that large grains, 
or large ears, or many ears per plant implied high yield. 
We may take it as definitely settled that none of these characters is 
reliable, and that the determination of yielding capacity resolves itself into the 
measurement of the yield given by a definite area. The actual measurement, 
therefore, is the same as that made in manurial trials, and is, of course, subject 
to the same probable error of about five per cent. 
It follows, therefore, that it is subject to the same limitations. Variety 
trials on single plots, and that is the method commonly used, will serve to 
measure variations in yielding capacity of thirty per cent., or more, but are 
totally inadequate to distinguish between varieties whose yielding capacities are 
within ten per cent. of each other. 
Numbers of such single-plot trials have been carried out, with the result that 
many varieties with yielding capacities much below normal have almost dis- 
appeared from cultivation, and those commonly grown do not differ greatly from 
one another—probably not more than ten per cent. 
Ten per cent. in yielding capacity, however, in cereals means a return of 
something like 15s. to 20s. per acre—a sum which may make the difference 
between profit and loss; and if progress is to be made in manuring and variety 
testing some method must be adopted which is capable of measuring accurately 
differences in yield per unit area of the order of ten per cent. 
The only way of decreasing the probable error is to increase the number of 
plots, and to arrange them so that plots between which direct comparison is 
necessary are placed side by side, so as to reduce as much as possible variations 
due to differences in soil. Thus it has been shown that with ten plots in five 
pairs the probable error on the average can be reduced to about one per cent., in 
which case a difference of from five to ten per cent. can be measured with 
considerable certainty. 
Such a method involves, of course, a great deal of trouble; but agricultural 
science has now reached that stage of development at which the obvious facts 
which can be demonstrated without considerable effort have been demonstrated, 
and further knowledge can only be acquired by the expenditure of continually 
increasing effort. In fact, the law of diminishing return holds here, as else- 
where. 
It appears, then, that for questions involving measurements of yield per 
unit area, such, for instance, as manurial or variety trials, further advance is 
not likely to be made without the expenditure of much more care than has been 
given to such work in the past. The question naturally arises: Is it worth 
while? I think the following instance shows that it is: 
Some years ago an extensive series of variety trials was carried out in Nor- 
folk, in which several of the more popular varieties of barley were grown side 
by side at several stations for several seasons. In all, the trial was repeated 
eleven times. As a final result it was found that Archer’s stiff-straw barley gave 
ten per cent. greater yield than any other variety included in the trials, and by 
repetition of the experiment the probable error was reduced to one and a half 
per cent. The greater yield of ten per cent., being over six times the probable 
error of the experiment, indicates practical certainty that Archer barley may 
be relied on to give a larger crop than any of the other varieties with which it 
was compared. One difficulty still remained. It was almost impossible to 
obtain anything like a pure strain of Archer barley. Samples of Archer sold for 
seed commonly contained twenty-five per cent. of other varieties. This difficulty 
