In many cases, especially
with the more recent cultivated species, man has deliberately chosen
variable forms, because of their greater promise. Thirdly, wide
variability is the most efficient means of acclimatization, and only
species with many elementary units would have offered the adequate
material for introduction into new countries.
From this discussion it would seem that it is more reasonable to assert
that variability is one of the causes of the success of cultivation,
than to assume that cultivation is a cause of variability [67] at large.
And this assumption would be equally sufficient to explain the existing
conditions among cultivated plants.
Of course I do not pretend to say that cultivated plants should be
expected to be less variable than in the wild state, or that swarms of
elementary species might not be produced during cultivation quite as
well as before. However the chance of such an event, as is easily seen,
cannot be very great, and we shall have to be content with a few
examples of which the coconut is a notable one.
Leaving this general discussion of the subject, we may take up the
example of the beets. The sugar-beet is only one type from among a horde
of others, and though the origin of all the single types is not
historically known, the plant is frequently found in the wild state even
at the present time, and the native types may be compared with the
corresponding cultivated varieties.
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