Further details of these experiments
need not be given. Suffice to say, that occasional crosses between
species do occur, and not even rarely, that they are easily recognized
as such and cannot be confused with cases of atavism, and that therefore
they give proof to the assumption that in the same way crosses
ordinarily occur also between varieties [203] of the same species, if
cultivated at small distances apart, say 40-50 meters or even more.
Vicinism therefore, may play a part in all such cultures, enough to
account for all the impurities observed in the nurseries or in
commercial seed-samples.
Of course this whole discussion is limited to such species as are not
only as a rule visited by insects, but are dependent on these visits for
their fertilization. Most of our garden-flowers are included in this
category. If not then we may expect to find the cultures and seeds pure,
irrespective of the distances between allied varieties, as for instance
with peas, which are known to be self-fertilizing. Another instance is
given by the barley. One of the most curious anomalous varieties of this
cereal, is the "Nepaul-barley," with its small adventitious flowers on
the palets or inner scales. It is a very old, widely cultivated sort,
which always comes true from seed, and which has been tested in repeated
experiments in my garden.
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