ubetzkoy
planted for experiment in the open ground several varieties of the
pear, but one alone, the _Poire sans Pepins_, withstood the cold of
winter.[768] We thus see that our fruit-trees, like distinct species of
the same genus, certainly differ from each other in their
constitutional adaptation to different climates.

With the varieties of many plants, the adaptation to climate is often
very close. Thus it has been proved by repeated trials "that few if any
of the English varieties of wheat are adapted for cultivation in
Scotland;"[769] but the failure in this case is at first only in the
quantity, though ultimately in the quality, of the grain produced. The
Rev. J. M. Berkeley sowed wheat-seed from India, and got "the most
meagre ears," on land which would certainly have yielded a good crop
from English wheat.[770] In these cases varieties have been carried
from a warmer to a cooler climate; in the reverse case, as "when wheat
was imported directly from France into the West Indian Islands, it
produced either wholly barren spikes or furnished with only two or
three miserable seeds, while West Indian seed by its side yielded an
enormous harvest."[771] Here is another case of close adaptation to a
slightly cooler climate; a kind of wheat which in England may be used
indifferently either as a winter or summer variety, when sown under the
warmer climate of Grignan, in France, behaved exactly as if it had been
a true winter wheat.[772]

Botanists believe that all the varieties of maize belong to the same
species; and we have seen that in North America, in proceeding
northward, the varieties cultivated in each zone produce their flowers
and ripen their seed within shorter and shorter periods. So that the
tall, slowly maturing southern varieties do not succeed in New England,
and the New English varieties do not succeed in Canada. I have not met
with any statement that the southern varieties are actually injured or
killed by a degree of cold which the northern varieties withstand with
impunity, though this is probable; but the production of early
flowering and early seeding varieties deserves to be considered as one
form of acclimatisation. Hence it has been found possible, according to
Kalm, to cultivate maize further and further northwards in America. In
Europe, also, as we learn fro