The
largest types are limited to temperate and subtropical regions, while
the varieties capable of cultivation in more northern latitudes are
smaller in size and stature and require a smaller number of days to
reach their full development from seed to seed. Northern varieties are
small and short lived, but the "Forty-day-corn" or "Quarantino maize" is
recorded to have existed in tropical America at the time of Columbus. In
preference, or rather to the entire exclusion of taller varieties, it
has thriven on the northern boundaries of the corn-growing states of
Europe since the very beginning of its cultivation.
According to Naudin, the same rule prevails with melons, cucumbers and
gherkins, and other instances could easily be given.
Referring now to the inferences that may be drawn from the experience of
the breeders in order to elucidate the natural processes, we will return
to the whitlow-grasses and pansies.
[119] Nature has constituted them as groups of slightly different
constant forms, quite in the same way as wheat and oats and corn.
Assuming that this happened ages ago somewhere in central Europe, it is
of course probable that the same differences in respect to the influence
of climatic conditions will have prevailed as with cereals. Subsequent
to the period which has produced the numerous elementary species of the
whitlow-grass came a period of widespread distribution.
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