Origin of Species Variorum

→ would travel further and further 1869 1872

travel 1859 1860 1861 1866

↑ 1 blocks not present in 1869 1872; present in 1859 1860 1861 1866

We may suppose that the Glacial period came on a little earlier or later in North America than in Europe, so will the southern migration there have been a little earlier or later; but this will make no difference in the final result.

→ as the warmth increased and the snow still further disappeared, higher and higher, 1866 1869 1872

higher and higher, as the warmth increased, 1859 1860 1861

→ together 1872

in a body together 1859 1860 1861

together in a body 1866 1869

→ European and North American lowlands, would again be found in the arctic regions of the Old and New Worlds, 1869 1872

lowlands of the Old and New Worlds, 1859 1860 1861

European and North American lowlands, 1866

→ and on many isolated mountain-summits far distant from each other. 1869 1872

would be left isolated on distant mountain-summits (having been exterminated on all lesser heights) and in the arctic regions of both hemispheres. 1859 1860 1861

would be found in the arctic regions of the Old and New Worlds, and isolated on many mountain-summits far distant from each other, having been exterminated on all lesser heights. 1866

→ first migration when 1866 1869 1872

migration as 1859 1860 1861

→ formerly permitted their 1866 1869 1872

permitted their former 1859 1860 1861

at the same

time

time,

→would travel further and further southward, unless they were stopped by barriers, in which case they would perish. The mountains would become covered with snow and ice, and their former Alpine inhabitants would descend to the plains. By the time that the cold had reached its maximum, we should have

a uniform

arctic fauna and flora, covering the central parts of Europe, as far south as the Alps and Pyrenees, and even stretching into Spain. The now temperate regions of the United States would likewise be covered by arctic plants and

animals,

animals

and these would be nearly the same with those of Europe; for the present circumpolar inhabitants, which we suppose to have everywhere travelled southward, are remarkably uniform round the world. ↑

As the warmth returned, the arctic forms would retreat northward, closely followed up in their retreat by the productions of the more temperate regions. And as the snow melted from the bases of the mountains, the arctic forms would seize on the cleared and thawed ground, always

ascending

ascending,

→as the warmth increased and the snow still further disappeared, higher and higher, whilst their brethren were pursuing their northern journey. Hence, when the warmth had fully returned, the same

arctic

....

species, which had lately lived →together on the →European and North American lowlands, would again be found in the arctic regions of the Old and New Worlds, →and on many isolated mountain-summits far distant from each other.

Thus we can understand the identity of many plants at points so immensely remote as

....

the mountains of the United States and

those of

Europe. We can thus also understand the fact that the Alpine plants of each mountain-range are more especially related to the arctic forms living due north or nearly due north of them: for the →first migration when the cold came on, and the

remigration

re-migration

on the returning warmth,

will

would

generally have been due south and north. The Alpine plants, for example, of Scotland, as remarked by Mr. H. C. Watson, and those of the Pyrenees, as remarked by Ramond, are more especially allied to the plants of northern Scandinavia; those of the United States to Labrador; those of the mountains of Siberia to the arctic regions of that country. These views, grounded as they are on the perfectly well-ascertained occurrence of a former Glacial period, seem to me to explain in so satisfactory a manner the present distribution of the Alpine and Arctic productions of Europe and America, that when in other regions we find the same species on distant mountain-summits, we may almost

conclude

conclude,

without other evidence, that a colder climate →formerly permitted their migration across the

low

....

intervening

tracts, since

lowlands, now

become too warm for their