days afterwards, and of the dozen plants which had previously escaped
only three survived; these were not taller or more vigorous than the other
young plants, but they escaped completely, with not even the tips of their
leaves browned. It was impossible to behold these three plants, with their
blackened, withered, and dead brethren all round them, and not see at a
glance that they differed widely in constitutional power of resisting
frost.

This work is not the proper place to show that wild plants {310} of the
same species, naturally growing at different altitudes or under different
latitudes, become to a certain extent acclimatised, as is proved by the
different behaviour of their seedlings when raised in England. In my
'Origin of Species' I have alluded to some cases, and I could add others.
One instance must suffice: Mr. Grigor, of Forres,[785] states that
seedlings of the Scotch fir (_Pinus sylvestris_), raised from seed from the
Continent and from the forests of Scotland, differ much. "The difference is
perceptible in one-year-old, and more so in two-year-old seedlings; but the
effects of the winter on the second year's growth almost uniformly makes
those from the Continent quite brown, and so damaged, that by the month of
March they are quite unsaleable, while the plants from the native Scotch
pine, under the same treatment, and standing alongside, although
considerably shorter, are rather stouter and quite green, so that the beds
of the one can be known from the other when seen from the distance of a
mile." Closely similar facts have been observed with seedling larches.

Hardy varieties would alone be valued or noticed in Europe; whilst
tender varieties, requiring more warmth, would generally be neglected;
but such occasionally arise. Thus Loudon[786] describes a Cornish
variety of the elm which is almost an evergreen, and of which the
shoots are often killed by the autumnal frosts, so that its timber is
of little value. Horticulturists know that some varieties are much more
tender than others: thus all the varieties of the broccoli are more
tender than cabbages; but there is much difference in this respect in
the sub-varieties of the broccoli; the pink and purple kinds are a
little hardier than the white Cape broccoli, "but they are not to be
depended on after the thermometer falls below 24deg Fahr.:" the
Walcheren broccoli is less tender than the Cape, and there a