Further it would seem only natural to explain the wide variability of
many of our larger agricultural and horticultural stocks by such an
incipient multiformity of the species themselves. Through commercial
intercourse the various types might have become mixed so as to make it
quite impossible to point out the native localities for each of them.
Unfortunately historical evidence on this point is almost wholly
lacking. The differences in question could not have been appreciated at
that remote period, and interest the common observer but little even
today. The history of most of the cultivated plants is very obscure,
[66] and even the most skillful historians, by sifting the evidence
afforded by the older writers, and that obtained by comparative
linguistic investigations have been able to do little more than frame
the most general outline of the cultural history of the most common and
most widely used plants.
Some authors assume that cultivation itself might have been the
principal cause of variability, but it is not proved, nor even probable,
that cultivated plants are intrinsically more variable than their wild
prototypes. Appearances in this case are very deceptive. Of course
widely distributed plants are as a rule richer in subspecies than forms
with limited distribution, and the former must have had a better chance
to be taken into cultivation than the latter.
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