But the most important result for us, arrived at by Mr.Croll, is that whenever the northern hemisphere passes through a cold period the temperature of the southern hemisphere is actually raised, with the winters rendered much milder, chiefly through changes in the direction of the ocean currents.

So conversely it will be with the northern hemisphere, while the southern passes through a glacial period.

This conclusion throws so much light on geographical distribution that I am strongly inclined to trust in it; but I will first give the facts which demand an explanation.
In South America, Dr.Hooker has shown that besides many closely allied species, between forty and fifty of the flowering plants of Tierra del Fuego, forming no inconsiderable part of its scanty flora, are common to North America and Europe, enormously remote as these areas in opposite hemispheres are from each other.

On the lofty mountains of equatorial America a host of peculiar species belonging to European genera occur.
On the Organ Mountains of Brazil some few temperate European, some Antarctic and some Andean genera were found by Gardner which do not exist in the low intervening hot countries.

On the Silla of Caraccas the illustrious Humboldt long ago found species belonging to genera characteristic of the Cordillera.
In Africa, several forms characteristic of Europe, and some few representatives of the flora of the Cape of Good Hope, occur on the mountains of Abyssinia.