In summers
which are unfavorable to the development of the cultivated oats it may
be observed to multiply with an almost incredible rapidity. It does not
contribute to the harvest, and is quite useless. If no selection were
made, or if selection were discontinued, it would readily supplant the
cultivated varieties.
From these several observations and experiments it may be seen, that it
is not at all easy to keep the common varieties of cereals pure and that
even the best are subject to the encroachment of impurities. Hence it is
only natural that races of cereals, when cultivated without the utmost
care, or even when selected without an exact knowledge of their single
constituents, are always observed to be more or less in a mixed
condition. Here, as everywhere with cultivated and wild plants, the
systematic species consist of a number of minor types, which pertain to
different countries and climates, and are growing together in the same
climate and under the same external conditions. They do not mingle, nor
are their differentiating characters destroyed by intercrossing. They
each remain pure, and may be isolated whenever and wherever the
desirability for such a proceeding should arise. The purity of [102] the
races is a condition implanted in them by man, and nature always strives
against this arbitrary and one-sided improvement.
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