I must now say a few words on what are called accidental means, but
which more properly might be called occasional means of distribution. I
shall here confine myself to plants. In botanical works, this or that
plant is stated to be ill adapted for wide dissemination; but for
transport across the sea, the greater or less facilities may be said to
be almost wholly unknown. Until I tried, with Mr. Berkeley s aid, a few
experiments, it was not even known how far seeds could resist the
injurious action of sea-water. To my surprise I found that out of 87
kinds, 64 germinated after an immersion of 28 days, and a few survived
an immersion of 137 days.
For convenience sake I chiefly tried small seeds, without the capsule
or fruit; and as all of these sank in a few days, they could not be
floated across wide spaces of the sea, whether or not they were injured
by the salt-water. Afterwards I tried some larger fruits, capsules,
etc., and some of these floated for a long time. It is well known what
a difference there is in the buoyancy of green and seasoned timber; and
it occurred to me that floods might wash down plants or branches, and
that these might be dried on the banks, and then by a fresh rise in the
stream be washed into the sea. Hence I was led to dry stems and
branches of 94 plants with ripe fruit, and to place them on sea water.
The majority sank quickly, but some which whilst green floated for a
very short time, when dried floated much longer; for instance, ripe
hazel-nuts sank immediately, but when dried, they floated for 90 days
and afterwards when planted they germinated; an asparagus plant with
ripe berries floated for 23 days, when dried it floated for 85 days,
and the seeds afterwards germinated: the ripe seeds of Helosciadium
sank in two days, when dried they floated for above 90 days, and
afterwards germinated. Altogether out of the 94 dried plants, 18
floated for above 28 days, and some of the 18 floated for a very much
longer period. So that as 64/87 seeds germinated after an immersion of
28 days; and as 18/94 plants with ripe fruit (but not all the same
species as in the foregoing experiment) floated, after being dried, for
above 28 days, as far as we may infer anything from these scanty facts,
we may conclude that the seeds of 14/100 plants of any country might be
floated by sea-currents during 28 days, and would retain their power of
germination. In Johnston s Physical Atlas, the average rate of the
several Atlantic currents is 33 miles per diem (some currents running
at the rate of 60 miles
per diem); on this average, the seeds of 14/100 plants belonging to one
country might be floated across 924 miles of sea to another country;
270