| ↑ 4 blocks not present in 1859 1860 1861 1866; present in 1869 1872 |
| The inhabitants of these lowlands
would at the same time migrate
to the tropical and sub-tropical regions of the south, for the southern hemisphere was at this period warmer.
On the decline of the Glacial period, as both hemispheres gradually recovered their former temperatures, the northern temperate forms living on the lowlands under the equator, would be
driven to their former homes or be
destroyed, being replaced by the equatorial forms returning from the south.
Some, however, of the northern temperate forms would almostc
ertainly
ascend
any adjoining high land, where, if sufficiently lofty, they would long
survive,
like the Arctic forms on the mountains of Europe.
They might survive,
even if the climate was not perfectly fitted for them, for the change of temperature must have been very slow, and plants undoubtedly possess a certain capacity for acclimatisation, as shown by their transmitting to their offspring different constitutional powers of resisting heat and cold.
|
|
| → Hence they will have 1866 |
| The tropical plants probably 1859 1860 1861 |
|
| → now see crowded together 1866 |
| see 1859 1860 1861 |
|
| → OMIT 1866 |
| present day crowded together at the 1859 1860 1861 |
|
| → lowest, most protected, and warmest districts. 1860 1861 1866 |
| warmest spots. 1859 |
|
| ↑ 1 blocks not present in 1866 1869 1872; present in 1859 1860 1861 |
| But the great fact to bear in mind is, that all tropical productions will have suffered to a certain extent.
|
|
| → that proper to them. 1866 |
| their own. 1859 1860 1861 |
|
|
humidity, &c.; and various animals and plants will have migrated in different proportions and at different rates. So that altogether during the Glacial period the inhabitants of the tropics must have been greatly disturbed in all their relations of life. ↑
→Hence they will have
suffered much extinction; how much no one can say; perhaps formerly the tropics supported as many species as we
→now see crowded together
at the
→OMIT
Cape of Good Hope, and in parts of temperate
As we know that many tropical plants and animals can withstand a considerable amount of cold, many might have escaped extermination during a moderate fall of temperature, more especially by escaping into the
→lowest, most protected, and warmest districts. Nor must it be overlooked that, as the cold will have come on very slowly, it is almost certain that many of the inhabitants of the tropics will have become in some degree acclimatised; in the same manner as the same species of plant when living on lowlands and highlands certainly transmit to their seedlings different constitutional powers of resisting cold. Nevertheless, it cannot be denied that all tropical productions will have greatly suffered, and the chief difficulty is to understand how they can have escaped entire annihilation. ↑
On the other hand, the temperate productions, after migrating nearer to the equator, though they will have been placed under somewhat new conditions, will have suffered less. And it is certain that many temperate plants, if protected from the inroads of competitors, can withstand a much warmer climate than
→that proper to them. Hence, it seems to me possible, bearing in mind that the tropical productions were in a suffering
and could not have presented a firm front against intruders, that a certain number of the more vigorous and dominant temperate forms might have penetrated the
|
