Running streams and ocean
currents also transport seeds from one locality to another. The
gulf-stream, as is well known, carries occasionally branches of trees
to the north coast of Scotland and Norway; and 'Mr Brown found that
six hundred plants collected about the river Zaire, in Africa,
included thirteen species, natives also of Guyana and Brazil. These
species mostly occurred near the mouth of the Zaire, and were of such
kind as produced fruits capable of resisting external agencies for a
long time.' Then, again, the agency of birds, of quadrupeds, and of
man, in the distribution of seeds and plants, is too important to be
overlooked, as Sir Charles Lyell has ably shewn in his _Principles of
Geology_; and there is 'a certain number of plants which seem to
accompany man wherever he goes, and to flourish best in his vicinity.
Thus, the docks, the goosefoots, the nettle, the chickweed, mallows,
and many other common weeds, seem to be universal, though unwelcome
companions to man--dogging his footsteps, affording by their presence,
even in now deserted districts, an almost certain index of the former
residence of human beings on the spot.'
From an examination of the causes affecting distribution, Mr Henfrey
passes to a survey of the characteristics of the countries of Europe,
from north to south--from the peninsula of Scandinavia to those of
Spain, Italy, and Greece.
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