many fresh-water and even marsh-species have, both over continents and
to the most remote oceanic islands. This is strikingly shown, as
remarked by Alph. de Candolle, in large groups of terrestrial plants,
which have only a very few aquatic members; for these latter seem
immediately to acquire, as if in consequence, a very wide range. I
think favourable means of dispersal explain this fact. I have before
mentioned that earth occasionally, though rarely, adheres in some
quantity to the feet and beaks of birds. Wading birds, which frequent
the muddy edges of ponds, if suddenly flushed, would be the most likely
to have muddy feet. Birds of this order I can show are the greatest
wanderers, and are occasionally found on the most remote and barren
islands in the open ocean; they would not be likely to alight on the
surface of the sea, so that the dirt would not be washed off their
feet; when making land, they would be sure to fly to their natural
fresh-water haunts. I do not believe that botanists are aware how
charged the mud of ponds is with seeds: I have tried several little
experiments, but will here give only the most striking case: I took in
February three table-spoonfuls of mud from three different points,
beneath water, on the edge of a little pond; this mud when dry weighed
only 6 3/4 ounces; I kept it covered up in my study for six months,
pulling up and counting each plant as it grew; the plants were
of many kinds, and were altogether 537 in number; and yet the viscid
mud was all contained in a breakfast cup! Considering these facts, I
think it would be an inexplicable circumstance if water-birds did not
transport the seeds of fresh-water plants to vast distances, and if
consequently the range of these plants was not very great. The same
agency may have come into play with the eggs of some of the smaller
fresh-water animals.
Other and unknown agencies probably have also played a part. I have
stated that fresh-water fish eat some kinds of seeds, though they
reject many other kinds after having swallowed them; even small fish
swallow seeds of moderate size, as of the yellow water-lily and
Potamogeton. Herons and other birds, century after century, have gone
on daily devouring fish; they then take flight and go to other waters,
or are blown across the sea; and we have seen that seeds retain their
power of germination, when rejected in pellets or in excrement, many
hours afterwards. When I saw the great size of the seeds of that fine
water-lily, the Nelumbium, and remembered Alph. de Candolle s remarks
on this plant, I thought that its distribution must remain quite
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