onette in Tasmania. On the other
hand, perennials sometimes become annuals, as with the Ricinus in England,
and as, according to Captain Mangles, with many varieties of the
heartsease. Von Berg[755] raised from seed of _Verbascum phoenicium_, which
is usually a biennial, both annual and perennial varieties. Some deciduous
bushes become evergreen in hot countries.[756] Rice requires much water,
but there is one variety in India which can be grown without
irrigation.[757] Certain varieties of the oat and of our other cereals are
best fitted for certain soils.[758] Endless similar facts could be given in
the animal and vegetable kingdoms. They are noticed here because they
illustrate analogous differences in closely allied natural species, and
because such changed habits of life, whether due to use and disuse, or to
the direct action of external conditions, or to so-called spontaneous
variation, would be apt to lead to modifications of structure.

* * * * *

_Acclimatisation._--From the previous remarks we are naturally led to the
much disputed subject of acclimatisation. There are two distinct questions:
Do varieties descended from the same species differ in their power of
living under different climates? And secondly, if they so differ, how have
they become thus adapted? We have seen that European dogs do not succeed
well in India, and it is asserted,[759] that no one has succeeded in there
keeping the Newfoundland long alive; but then it may be argued, probably
with truth, that these northern breeds are specifically distinct from the
native dogs which flourish in India. The same remark may be made with
respect to different breeds of sheep, of which, according to Youatt,[760]
not one brought "from a torrid climate lasts out the second year," in the
Zoological Gardens. But sheep are capable of some degree of
acclimatisation, for Merino sheep bred at the Cape of Good Hope have been
found {306} far better adapted for India than those imported from
England.[761] It is almost certain that the breeds of the fowl are
descended from the same species; but the Spanish breed, which there is good
reason to believe originated near the Mediterranean,[762] though so fine
and vigorous in England, suffers more from frost than any other breed. The
Arrindy silk-moth introduced from Bengal, and the Ailanthus moth from the
temperate province of Shan Tung, in China, belong to the same species, as
we may infer fr