82 Variation 
or two exceptions. A few lots showed a perfect uniformity in regard 
to all the stalks and ears: these were small families. This fact 
suggested the idea that each might have been derived from a single 
ear. During the selection in the previous summer, Nilsson had tried 
to find as many ears as possible of each new type which he recognised 
in his fields. But the variability of his crops was so great, that 
he was rarely able to include more than two or three ears in the 
same group, and, in a few cases, he found only one representative 
of the supposed type. It might, therefore, be possible that those 
small uniform plots were the direct progeny of ears, the grains of 
which had not been mixed with those from other ears before sowing. 
Exact records had, of course, been kept of the chosen samples, 
and the number of ears had been noted in each case. It was, there- 
fore, possible to answer the question and it was found that those 
plots alone were uniform on which the kernels of one single ear 
only had been sown. Nilsson concluded that the mixture of two or 
more ears in a single sowing might be the cause of the lack of uni- 
formity in the progeny. Apparently similar ears might be different 
in their progeny. 
Once discovered, this fact was elevated to the rank of a leading 
principle and tested on as large a scale as possible. The fields were 
again carefully investigated and every single ear, which showed a 
distinct divergence from the main type in one character or another, 
was selected. A thousand samples were chosen, but this time 
each sample consisted of one ear only. Next year, the result 
«eorresponded to the expectation. Uniformity prevailed almost every- 
where; only a few lots showed a discrepancy, which might be 
ascribed to the accidental selection of hybrid ears. It was now clear 
that the progeny of single ears was, as a rule, pure, whereas that of 
mixed ears was impure. The single-ear selection or single-ear sowing, 
which had fallen into discredit in Germany and elsewhere in Europe, 
was rediscovered. It proved to be the only trustworthy principle of 
selection. Once isolated, such single-parent races are constant 
from seed and remain true to their type. No further selection is 
needed ; they have simply to be multiplied and their real value 
tested. 
Patrick Shirreff, in his early experiments, Le Couteur, Hays and 
others had observed the rare occurrence of exceptionally good 
yielders and the value of their isolation to the agriculturist. The 
possibility of error in the choice of such striking specimens and the 
necessity of judging their value by their progeny were also known to 
these investigators, but they had not the slightest idea of all the 
possibilities suggested by their principle. Nilsson, who is a botanist 
as well as an agriculturist, discovered that, besides these exception- 
