WATER TRANSPORTATION OF PLANTS.
11. Some green buds and leaves float on water.--Loosely floating on
slow streams of the northern states, in water not the purest, may
often be found the common bladderwort, _Utricularia vulgaris_,
producing in summer a few yellow flowers on each stem, rising from
six to twelve inches above the water. The lax, leafy branches in the
water are from six inches to a foot long. The leaves, or thread-like
branches, are about half an inch long, more or less, and several times
divided.
[Illustration: FIG. 11.--A free branch and two buds of bladderwort.]
Scattered about are large numbers of flattened scales, or bladders,
sometimes one-sixth of an inch long, which give the plant one of its
names. For a long time the bladders were thought to serve merely as
life-preservers; it was supposed that they were constructed to keep
the plant from sinking to the bottom. In reality these bladders help
preserve the plant in another sense, by catching and killing large
numbers of minute animals, on which the plant lives in part. The tips
of the stems at all times of the year are rather compact, made up
of young leaves and stems, and in the middle of the summer, as well
as at other times, many may be seen severed from the parent plant,
floating in the water, ready to accept the assistance of any favorable
current or breeze and start out for homes of their own to found new
colonies. These olive-green tips, or buds, vary much in size, but
the largest are the size of the end of one's little finger. Late in
autumn or early winter, when cold threatens, the tender buds contract
a little, and, having thus become heavier than water, slowly go to the
bottom to spend the winter safely protected in the soft mud. All the
plant perishes except these buds. With the lengthening days of spring
the melting ice disappears, and genial sunshine gives notice to the
dormant buds that it is safe to come out again. The buds begin to
expand, become lighter than water, and are soon seen spreading out at
the surface and producing branches and leaves. Ducks and other
water-fowl not infrequently carry some of these wet buds sticking to
their feathers or legs.
In this connection the following plants may be examined from time
to time: _Lemna_, _Wolffia_, _Anacharis_ (_Elodea_), _Myriophyllum_,
_Cabomba_, and several species of _Potamogeton_. I have seen the
leaves of lake cress, _Nasturtium lacustre_, often spontaneously
separate from the stem, possibly carrying at the base the rudiments
of a small bud, which draws on the floating leaf for nourishment and
produces a small plant near its base. These plants, floated and
nourished by the mother leaf, may drift down a creek or across a pond
and establish new settlements. In a similar manner behave leaves of
the following, and perhaps others: _Cardamine pratensis_,
horse-radish, celandine, some water lilies, and other plants not
grown in wet land.
[Illustration: FIG. 12.--Floating leaf of lake cress, _Nasturtium
lacustre_, with a young plant growing from the base.]
Gardeners often propagate certain species by placing leaves on wet
sand or mud, when buds spring from the margins of the leaves or from
some other portion.
One of the buttercups, _Ranunculus multifidus_, and very likely
others, spread over the mud by producing runners, much after the
manner of a strawberry plant. If, as in case of a freshet, the plants
should be covered with water, they show their enterprise by taking
advantage of the "tide"; some of the runners are quickly severed,
and are then at liberty to go as they please.
12. Fleshy buds drop off and sprout in the mud.--One of the
loosestrifes, _Lysimachia stricta_, a plant growing in bogs, besides
reproducing itself by rootstocks and seeds, bears fleshy buds half
an inch long, which separate from the stems and take root in the mud
near the parent plant, or often float to another spot. The buds on
the stems of _Cicuta bulbifera_ develop into small bulbs, which
readily separate from the plant. They then float on the water and
produce new plants. The tiger lily also produces bulblets, which
scatter about and promptly take root. Every person of good
understanding must have heard or read about seeds carried by ocean
currents or transported by lake, pond, creek, or by muddy current,
during, and after, a shower of rain; in most of these the wind is
also a prominent factor. Many seeds and fruits, in some cases parts,
and even the whole, of plants seem to be purposely designed for this
mode of travel, while an innumerable host of others occasionally make
use of it, although it may seem from their structure and place of
growth that they were made especially to be transported by the wind
or by some animal. As has been seen in examples previously mentioned,
one portion of a plant is transported in one way, and another portion
by one or two other methods.
[Illustration: FIG. 13.--Branch of loosestrife bearing tuber
bulblets.]
[Illustration: FIG. 14.--One of the tubers enlarged.]
13. Seeds and fruits as boats and rafts.--An excellent place in which
to begin investigating this part of the subject is to pay a visit
to the flats of a creek or river late in autumn or in the spring,
after the water has retired to its narrow channel, and examine piece
after piece of the rubbish that has been lodged here and there against
a knoll or some willows, a patch of rushes or dead grass. We are
studying the different modes by which plants travel. In the driftwood
may be found dry fruits of the bladder nut, brown and light, an inch
and a half in diameter. See how tough they are; they seem to be
perfectly tight, and even if one happens to have a hole punched in
its side, there are probably two cells that are still tight, for there
are three in all. Within are a few seeds, hard and smooth. Why are
they so hard? Will it not be difficult for such seeds to get moist
enough and soft enough to enable them to germinate? The hard coats
enable the seeds to remain uninjured for a long time in the water,
in case one or two cells of the papery pods are broken open; and after
the tough pod has decayed and the seeds have sunken to the moist earth
among the sticks and dead leaves, they can have all the time they
need for the slow decay of their armor. Sooner or later a tiny plant
is likely to appear and produce a beautiful bush. Engineers are
boasting of their steel ships as safe and not likely to sink, because
there are several compartments each in itself water-tight. In case
of accident to one or two chambers, the one or two remaining tight
will still float the whole and save the passengers.
[Illustration: FIG. 15.--Fruit of bladder nut with three tight
cells.]
I wonder if the engineers have not been studying the fruit of the
bladder nut? But this is not all. Many of the dry nuts hang on all
winter, or for a part of it, rattling in the wind, as though loath
to leave. Some of them are torn loose, and in winter there will be
a better chance than at any other time for the wind to do the seeds
a favor, especially when there is snow on the ground, for then they
will bound along before the breeze till something interrupts them.
Here among the rubbish are some shriveled wild grapes also. As we
shall see elsewhere, their best scheme is to be eaten by certain birds,
which do not digest their bony seeds; but in case some of them are
left there is another mode of travel, not by wings of a bird, but
by floating on water.
[Illustration: FIG. 16.--Shriveled wild grapes overlooked by birds,
now ready to float on water, and a clean seed not able to float.]
Clean grape seeds sink at once, but covered by the dry skin and pulp,
they float. In a similar manner the dry seeds of several dogwoods
are eaten for the pulp by birds, but in case any are left they behave
after the manner of grapes.
14. Bits of cork around the seeds prevent them from
sinking.--Narrow-leaved dock is a prominent weed, and is especially
at home on river bottoms and on low land that is flooded once in a
while.
[Illustration: FIG. 17.--Fruit and adherent calyx of narrow-leaved
dock; a cross section and a naked, seed-like fruit (enlarged).]
Did you ever wonder what could be the object of a round, spongy
tubercle on the outside of each of these sepals which hold the ripened
seed closely? I did not know their use for a long time, but now think
I have discovered their meaning. They are not exactly life-preservers,
but the next thing to it. The naked, seed-like fruit, the shape of
the fruit of buckwheat, sinks at once when free from everything else,
but with the dry calyx still attached, it floats with the stream.
15. An air-tight sack buoys up seeds.--Here are several dry fruits
of sedges--plants looking considerably like grasses. There are a good
many kinds, and most of them grow in wet places. The seed-like fruit
of those we examine are surrounded each by a sack which is considerably
too large for it, as one would be likely to say, but in reality it
serves to buoy the denser portion within, much after the plan of the
bladder nut. In some instances the sack is rather small, but a corky
growth below the grain helps to buoy it on water.
[Illustration: FIG. 18.--Fruit of Asa-Gray sedge with an inflated
sack about it.]
Sedges that grow on dry land usually have the sack fitted closely,
instead of inflated, and the whole mass sinks readily in water. Now
we see the probable reason why the sack is inflated in some species
of sedges and not in others.
[Illustration: FIG. 19.--Fruit of _Carex communis_, an upland sedge,
that readily sinks when placed in water; the sack fits closely.]
Here are some small, seed-like fruits, _achenes_, not likely to be
recognized by every one. They belong to the arrowhead, _Sagittaria_,
found in shallow ponds or slow streams. They are flattened, and on
one edge, or both, and at the apex is a spongy ridge. Very likely,
by this time, the reader has surmised that this serves the purpose
of a raft to float the small seed within, which would sink at once
if separated from the boat that grew on its margins. In this connection
may be studied achenes of water plantain, _Alisma_, bur reed,
cat-tail flag, arrow grass, burgrass, numerous pondweeds, several
buttercups, the hop, nettles, wood nettle, false nettle, cinquefoil,
avens, ninebark, buttonbush, and in fact a large number and variety
of plants usually found on river bottoms.
[Illustration: FIG. 20.--Seed-like fruit of arrowhead with corky
margins to float on water.]
[Illustration: FIG. 21.--Seed-like fruit of bur reed with corky
lining ready to float on water, and a naked seed, such as sinks
promptly.]
One of the lyme grasses, _Elymus Virqinicus_, is a stiff, short grass,
growing along streams. Each spikelet with its chaff adheres to two
empty glumes, stout, thick, and spongy, which make a safe double boat
for transportation down stream whenever the water is high enough.
The grains of rice-cut grass, grown in ditches and spring brooks,
sink if separated, but in the chaff, as they fall when ripe, they
are good floaters.
[Illustration: FIG. 22.--Grains of lyme grass with two corky empty
glumes attached, which serve as a raft.]
In the driftwood, which we still have under consideration, are some
fruits of maple, beech, oak, tulip tree, locust, and basswood. Maples
are well scattered by the wind, but these seed-like fruits have taken
to the water, and a few still retain vitality. An acorn, while yet
alive, sinks readily, and is not suited for water navigation, unless
by accident it rides on some driftwood. The fruits of the tulip tree,
locust, and basswood behave well on the water, as though designed
for the purpose, though we naturally, and with good reason, class
them with plants usually distributed by wind.
16. Fruit of basswood as a sailboat, and a few others as adapted to
the water.--In spring, when the bracts and fruits of the basswood
are dry and still hanging on the tree, if a quantity of them are shaken
off into the water which overflows the banks of a stream, many of
these, as they reach the water, will assume a position as follows:
The nuts spread right and left and float; the free portion of the
bract extends into the water, while the portion adhering to the
peduncle rises obliquely out of the water and serves as a sail to
draw along the trailing fruit. After sailing for perhaps fifteen
minutes, the whole bract and stem go under water, the nuts floating
the whole as they continue to drift with the wind.
Noticeable among seeds in the flood wood are some of the milkweeds,
which every one would say at a glance were especially fitted for
sailing through the air, aided by their numerous long, silky hairs.
These hairs are no hindrance to moving by water. I discovered one
little thing in reference to the seed which makes me think the Designer
intended it should to some extent be carried by water. The flat seed
has a margin, or hem, which must be an aid to the wind in driving
it about; but this margin is thickened somewhat by a spongy material.
[Illustration: FIG. 23.--Seed of milkweed with a corky margin
enabling it to float; a seed with such margin removed sinks at once.]
With the margin it floats, without it the seed sinks in fresh water.
A few cranberries were found in the driftwood. These contain
considerable air in the middle, near where the seeds are placed, as
though the air was intended to support them on top of water.
[Illustration: FIG. 24.--Cranberry containing an air space which
helps it to float.]
These berries are colored and edible--qualities that attract the
birds. And here we find in several places the bulblets of a wild garlic,
_Allium Canadense_, which grows on the river bottom. These bulblets
are produced on top of the stem with the flowers, and float on the
water. The seeds of the white water lilies, and yellow ones also,
by special arrangement float about on the water with the current or
the wind. The coffee tree grows rather sparingly along some of the
streams, and on moist land as far north as Clinton County, Michigan.
The stout, hard pods are three to four inches long, one and one-quarter
to one and one-half inches wide, and one-half inch thick. The very
hard seeds are surrounded with sweet pulp, which most likely made
it an inducement for some of our native animals to devour them and
thus transport the undigested seeds to remote localities. The pods
often remain on the trees all winter, and when dry, will float on
the water of overflowed streams without any injury resulting to the
hard seeds. By themselves the seeds sink at once.