s that a very small portion of mud may
serve to convey seeds, and such an occurrence repeated even at long
intervals may greatly aid in stocking remote islands with vegetation.
Many seeds also adhere to the feathers of birds, and thus, again, may be
conveyed as far as birds are ever carried. Dr. Guppy found a small hard
seed in the gizzard of a Cape Petrel, taken about 550 miles east of
Tristan da Cunha.
_Dispersal of Seeds by the Wind._
In the preceding cases we have been able to obtain direct evidence of
transportal; but although we know that many seeds are specially adapted
to be dispersed by the wind, we cannot obtain direct proof that they are
so carried for hundreds or thousands of miles across the sea, owing to
the difficulty of detecting single objects which are so small and
inconspicuous. It is probable, however, that the wind as an agent of
dispersal is really more effective than any of those we have hitherto
considered, because a very large number of plants have seeds which are
very small and light, and are often of such a form as to facilitate
aerial carriage for enormous distances. It is evident that such seeds
are especially liable to be transported by violent winds, because they
become ripe in autumn at the time when storms are most prevalent, while
they either lie upon the surface of the ground, or are disposed in dry
capsules on the plant ready to be blown away. If inorganic particles
comparable in weight, size, or form with such seeds are carried for
great distances, we may be sure that seeds will also be occasionally
carried in the same way. It will, therefore, be necessary to give a few
examples of wind-carriage of small objects.
On 27th July 1875 a remarkable shower of small pieces of hay occurred at
Monkstown, near Dublin. They appeared floating slowly down from a great
height, as if falling from a dark cloud which hung overhead. The pieces
picked up were wet, and varied from single blades of grass to tufts
weighing one or two ounces. A similar shower occurred a few days earlier
in Denbighshire, and was observed to travel in a direction contrary to
that of the wind in the lower atmosphere.[174] There is no evidence of
the distance from which the hay was brought, but as it had been carried
to a great height, it was in a position to be conveyed to almost any
distance by a violent wind, had such occurred at the time.
_Mineral Matter carried by the Wind._
The numerous cases of sand and vo
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