{368} <Note in original.> Perhaps vitality checked by cold and so
prevented germinating. <On the carriage of seeds by icebergs, see
_Origin_, Ed. i. p. 363, vi. p. 513.>

I will only hazard one other observation, namely that during the change
from an extremely cold climate to a more temperate one the conditions,
both on lowland and mountain, would be singularly favourable for the
diffusion of any existing plants, which could live on land, just freed
from the rigour of eternal winter; for it would possess no inhabitants;
and we cannot doubt that _preoccupation_{369} is the chief bar to the
diffusion of plants. For amongst many other facts, how otherwise can we
explain the circumstance that the plants on the opposite, though
similarly constituted sides of a wide river in Eastern Europe (as I was
informed by Humboldt) should be widely different; across which river
birds, swimming quadrupeds and the wind must often transport seeds; we
can only suppose that plants already occupying the soil and freely
seeding check the germination of occasionally transported seeds.

{369} A note by the author gives "many authors" apparently as
authority for this statement.

At about the same period when icebergs were transporting boulders in N.
America as far as 36 deg. south, where the cotton tree now grows in South
America, in latitude 42 deg. (where the land is now clothed with forests
having an almost tropical aspect with the trees bearing epiphytes and
intertwined with canes), the same ice action was going on; is it not
then in some degree probable that at this period the whole tropical
parts of the two Americas possessed{370} (as Falconer asserts that
India did) a more temperate climate? In this case the Alpine plants of
the long chain of the Cordillera would have descended much lower and
there would have been a broad high-road{371} connecting those parts of
North and South America which were then frigid. As the present climate
supervened, the plants occupying the districts which now are become in
both hemispheres temperate and even semi-tropical must have been driven
to the Arctic and Antarctic{372} regions; and only a few of the loftiest
points of the Cordillera can have retained their former connecting
flora. The transverse chain of Chiquitos might perhaps in a similar
manner during the ice-action period have served as a connecting road
(though a broken one) for Alpine plants to become dispersed from the
Cordi