Physical surroundings rather than latitude determine the character of the flora.

As a rule, the elevation of the timber line on the mountains increases as the latitude decreases.

Even so small an area as that of Britain illustrates what has already been pointed out, that the species of a flora change both with latitude and altitude.

But during the summer, temperatures are affected as much by altitude as by latitude, and the coast is cooled at night by breezes from the Gulf.

North of the North Atlantic maximum the waters become steadily fresher as latitude increases until the channels opening into the Arctic basin are reached.