orida, and
thence into the North American ocean, where it lies very thick on the
surface of the sea."[857]

The absence of liquid matter in the composition of seeds renders them
comparatively insensible to heat and cold, so that they may be carried
without detriment through climates where the plants themselves would
instantly perish. Such is their power of resisting the effects of heat,
that Spallanzani mentions some seeds that germinated after having been
boiled in water.[858] Sir John Herschel informs me that he has sown at
the Cape of Good Hope the seeds of the _Acacia lophanta_ after they had
remained for twelve hours in water of 140 degrees Fahrenheit, and they
germinated far more rapidly than unboiled seeds. He also states that an
eminent botanist, Baron Ludwig, could not get the seeds of a species of
cedar to grow at the Cape till they were thoroughly boiled.

When therefore, a strong gale, after blowing violently off the land for
a time, dies away, and the seeds alight upon the surface of the waters,
or wherever the ocean, by eating away the sea-cliffs, throws down into
its waves plants which would never otherwise reach the shores, the tides
and currents become active instruments in assisting the dissemination of
almost all classes of the vegetable kingdom. The pandanus and many other
plants have been distributed in this way over the islands of the
Pacific. I have before called attention (p. 618.) to the interesting
fact that one-fifth of all the algae found in the antarctic regions in
1841-3, by Dr. J. Hooker, were of species common to the British seas. He
has suggested that cold currents which prevail from Cape Horn to the
equator, and are there met by other cold water, may by their direct
influence, as well as by their temperature, facilitate the passage of
antarctic species to the Arctic Ocean. In like manner the migration of
certain marine animals from the southern to the northern hemisphere may
have been brought about by the same cause.

In a collection of six hundred plants from the neighborhood of the river
Zaire, in Africa, Mr. Brown found that thirteen species were also met
with on the opposite shores of Guiana and Brazil. He remarked that most
of these plants were found only on the lower parts of the river Zaire,
and were chiefly such as produced seeds capable of retaining their
vitality a long time in the currents of the ocean. Dr. J. Hooker informs
me that after an examination of a great many insu