PLANTS THAT ARE CARRIED BY ANIMALS.
With the frosts of autumn ripe acorns, beechnuts, bitternuts,
butternuts, chestnuts, hickory nuts, hazelnuts, and walnuts are
severed from the parent bush or tree and fall to the ground among
the leaves.
37. Squirrels leave nuts in queer places and plant some of them.--Even
before the arrival of frosts many of these are dropped by the aid
of squirrels, gray and red, which cut the stems with their teeth.
The leaves, with the help of the shifting winds, gently cover the
fruit, or some portions of it, and make the best kind of protection
from dry air and severe cold; and they come just in the nick of time.
Dame Nature is generous. She produces an abundance; enough to seed
the earth and enough to feed the squirrels, birds, and some other
animals. The squirrels eat many nuts, but I have seen them carry a
portion for some distance in several directions, and plant one or
two or three in a place, covering them well with soil. It may be the
thought of the squirrel--I cannot read his thoughts--to return at
some future time of need, as he often does. But in some cases he forgets
the locality, or does not return because he has stored up more than
he needs; or in some cases the squirrels leave that locality or are
killed; in any such case the planted nuts are not disturbed. At all
events, some of the nuts--one now and then is all that is needed--are
allowed to remain where planted. In this way the squirrel is a benefit
to the trees and pays for the nuts he eats. He has not lived in vain,
for he is a tree planter and believes in arboriculture. His arbor
day comes in autumn, and he needs no message from the governor to
stimulate him to work.
After some red squirrels had been given black walnuts, a member of
my family saw them hide the nuts in all conceivable places, and in
some instances place them above a cluster of small branches of a tree
for support where three or more twigs spread from nearly the same
place. Here the nuts, one in a place, were left till perhaps shaken
to the ground by a severe wind or by some other cause. In one winter,
without hunting for them, six to ten places were found in one
neighborhood of Michigan, where something had placed a single walnut
or acorn in the forks of small branches. In some cases a severe wind
could have dislodged the nut.
[Illustration: FIG. 49.--A black walnut as left by a red squirrel
on a small oak tree.]
On February 18, 1897, I found a single black walnut held by small
branches of a red oak.
The oak was an inch and a half in diameter, and the nut was about
six feet from the ground. The nearest bearing tree was fully three
hundred long steps distant. We can imagine that, through fright or
other causes, a squirrel might be suddenly interrupted while carrying
nuts, and might then drop them to the ground, where later a tree would
be started.
38. Birds scatter nuts.--The work of birds in scattering seeds and
fruits has long been recognized.[3]
[Footnote 3: In the fall of 1897, Prof. C. F. Wheeler saw a blue jay
fly from a white oak tree with an acorn in its mouth. The bird went
to the ground four or five rods distant and crowded the acorn into
the soil as far as it could, covering the spot with a few leaves.
A member of my family saw a blue jay leave half of a black walnut
in the forks of several small branches.]
Some friends of mine collected a quantity of hazelnuts, while yet
the green husks enclosed the nuts, and placed them near the house
to dry. At once they were discovered by a blue jay, which picked out
a nut at a time, flew away, held the nut between its toes, cracked
it from the small end, and ate the contents. In this operation a number
of nuts slipped away and were lost. But it seems that all were not
eaten, for the next season half a dozen or more hazel shoots came
up, and to-day a new patch of hazel bushes is growing in the yard.
Doubtless many acorns are carried from place to place and dropped
in an aimless way by woodpeckers, blue jays, and crows; also beechnuts
by these birds, and by nuthatches, and by pigeons, before the latter
became nearly extinct. Woodpeckers and blue jays place beechnuts and
small acorns in the crevices of bark on standing trees. If left there
very long, the nuts will become too dry to grow, but in the act of
transporting them some of the nuts may be accidentally dropped in
various places.
39. Do birds digest all they eat?--To determine whether seeds would
lose their vitality in passing through the digestive organs of birds,
Kerner von Marilaun fed seeds of two hundred and fifty different
species of plants to each of the following: blackbird, song thrush,
robin, jackdaw, raven, nutcracker, goldfinch, titmouse, bullfinch,
crossbill, pigeon, fowl, turkey, duck, and a few others; also to
marmot, horse, ox, and pig, making five hundred and twenty separate
experiments. As to the marmot, horse, ox, and pig, almost all the
fruits and seeds were destroyed. From the ox grew a very few seeds
of millet, and from the horse one or two lentils and a few oats; from
the pig a species of dogwood, privet, mallow, radish, and common
locust. Under ordinary conditions, no seed was found to germinate
after passing through the turkey, hen, pigeon, crossbill, bullfinch,
goldfinch, nutcracker, titmouse, and the duck. Ravens and jackdaws
passed without injury seeds of stone fruits and others with very hard
coats. Of seeds that passed through the blackbird 75 per cent
germinated, 85 per cent in the case of the thrush, 80 per cent in
the case of the robin.[4]
[Footnote 4: It should be noted that the blackbird here mentioned
is not the same as either of our blackbirds, but a thrush much like
our robin; that the robin mentioned is a ground warbler nearly related
to our bluebird. It should also be noted that jackdaws, ravens,
thrushes, and probably many others eject thousands of seeds by the
mouth for one which passes through the intestines.]
40. Color, odor, and pleasant taste of fruits are advertisements.--In
summer, buds are formed on bushes of black raspberry, blossoms appear,
and these are followed by small, green, and bitter berries, which
hardly anything cares to eat. They grow slowly, become soft and pulpy,
and finally good to eat. How is bird or boy or girl to know where
they are and when they are fit to eat? The plant has enterprise and
has displayed two want advertisements by painting the berries first
dark red, and then dark purple, when they are good to eat. But is
the plant made expressly to produce berries, just to feed birds and
children? If that be all, why are seeds formed in the berries in such
large numbers? No! They produce berries that contain seeds, and from
these seeds are to grow more bushes. Then why should not the berries
always remain bitter or hard, so that nothing would touch them? If
we may say so, the plant produces sweet and showy berries on purpose
to be eaten, that the seeds may be carried away. What becomes of the
seeds? Each one is enclosed in a hard, tough covering, which protects
it from destruction in the stomachs of many birds and some other
animals. The seeds are well distributed by the animals that eat the
berries. The brilliant colors of ripe berries say to bird and child:
"Here we are; eat us, for we are good." The sweet pulp pays the birds
for distributing the seeds, else they would not be so distributed.
The seeds are as well provided for locomotion as the ticks, the mites,
and the spiders, and when ready to go, the berries flaunt their colors
to attract attention. You see, then, that although the old parent
bush cannot change its place, young bushes grow from the tips of the
branches, and seedlings spring up at long distances from their old
homes.
[Illustration: FIG. 50.--Raspberry, ripened, picked, and ready to
be eaten.]
Sparrows, finches, and similar birds in the winter eat and destroy
seeds of grasses and weeds, while the same birds in summer and autumn
eat bushels of blueberries, huckleberries, elderberries,
raspberries, strawberries, and similar fruits, and distribute their
unharmed seeds over thousands of acres, which otherwise might never
support a growth of these species.
The downy woodpecker, among other things, devours berries of three
kinds of dogwood, Virginia creeper, service berry, strawberry,
pokeberry, poison ivy, poison sumac, stag-horn sumac, and blue beech.
The hairy woodpecker devours many of the above fruits, as well as
those of spicebush, sour gum, cherries, grapes, blackberries. The
flicker devours most of the fruits listed for the two woodpeckers
named above, also hackberry, black alder, green brier, bayberries.
A number of other woodpeckers possess habits much the same as the
three above named. The cedar bird devours many species of hard-seeded
fruits.
The various shades of red appear to good advantage among green leaves.
As illustrations of such, we have the wintergreen, partridge berry,
bush cranberry, bearberry, service berry, currant, holly, strawberry,
red-berried elder, winter berry, honeysuckle, and many more. Where
the leaves are liable to become red in autumn the berries are often
blue. Of such, notice wild grapes, blueberries, and berries of
sassafras, though the flowering dogwood has red leaves as well as
red berries.
There is a reason for prickles on rosebushes. When ripe, rosehips
are usually red or yellow, and thus attract birds which are fond of
the fleshy portion outside; but the seed-like nuts are too hard and
dry to suit their taste, and are rejected and sown in the vicinity,
where the ripened hips are picked in pieces and eaten. Mice and red
squirrels are also fond of the seed-like nutlets of roses, but seldom
secure them from the bushes. Why, do you ask? Because the prickles
were most likely placed on the rosebushes to prevent this very thing,
and not to annoy the lover of flowers, or to prevent her from cutting
what she needs.
41. The meddlesome crow lends a hand.--"One of the most industrious
and persistent seed-transporting agencies I know of is that
ubiquitous, energetic, rollicking, meddlesome busybody, the crow.
I have seen crows gather by hundreds and have a regular powwow, a
mass convention, where they seemed to discuss measures and appoint
officers. At length they get through, and as they start to fly away
many, if not all, will drop something. I have found these to be acorns,
walnuts, hickory nuts, buckeyes, sycamore balls, sticks, eggshells,
pebbles, etc. As a crow leaves an oak he will pluck an acorn, which
he may carry five miles and light on a beech tree where something
else will attract his attention, when he will drop the acorn and maybe
pluck a pod of beechnuts and fly away somewhere else."--_Prof.
W. B. Barrows_.
The number of seeds distributed by crows is enormous, and consists
of many species, including poison ivy and poison sumac, wild cherry,
dogwood, red cedar, sour gum, and Virginia creeper. The hard,
undigested seeds are mostly expelled from the mouth in pellets, shown
in the illustration, and germinate more promptly than those untouched
by birds.
[Illustration: FIG. 51.--Two views of a pellet of seeds and rubbish
from a crow. From bulletin No. 6, United States Department of
Agriculture, Division of Ornithology and Mammology.]
Bears are very fond of berries, and will scatter the seeds of service
berries, elder berries, chokecherries, raspberries, and
blackberries.
42. Ants distribute some kinds of seeds.--Ants are numerous, strong,
skillful, and in suitable weather are always very busy. Their habits
have been investigated, and it has been found that in some respects
they are genuine farmers on a small scale. They have their slaves
(not hired help); they feed their plant lice, remove them from place
to place, and otherwise care for them, because the lice constitute
one of the chief sources of their supply of sweet. They build roads
and houses, and enjoy society after their fashion. They have use for
certain kinds of seeds, portions or all of which they eat at once
or carry to their homes. A number of persons in different countries
and at different times have seen ants carrying seeds. Some young
student of botany may have noticed along one side of the glossy seeds
of the bloodroot a delicate, fleshy ridge, and wondered what could
be its use. The answer can now be given with a good degree of confidence.
The ants either eat this fleshy ridge at once, or, as more frequently
happens, carry such seeds to their homes. The smooth seeds they do
not eat, but cast them out of their nests after using the part they
like; after being rejected the seed may stand a chance to germinate.
The seeds cannot be carried so well unless this ridge, _caruncle_,
be present. Other seeds of this nature are those of wild ginger,
celandine, cyclamen, violet, periwinkle, some euphorbias, bellwort,
trillium, prickly poppy, dutchman's breeches, squirrel-corn,
several species of Corydalis, Seneca snakeroot, and other species
of milkworts.
[Illustration: FIG. 52.--Seed of bloodroot with caruncle or crest,
which serves as a handle for ants to hold on to. Ant ready to take
the seed.]
[Illustration: FIG. 53.--A view of a seed of euphorbia with a soft
bunch at one end, a handle for ants.]
In his work on _Vegetable Mold and Earthworms_, p. 113, Darwin states
that earthworms are in the habit of lining their holes, using seeds
among other things, and that these sometimes grow. In this way the
worms aid in spreading plants.
43. Cattle carry away living plants and seeds.--In Arizona, where
cacti abound, Professor Toumey finds that many of them are broken
in pieces by cattle, which eat a portion, while other portions often
adhere to the legs or noses and are carried from place to place. These
fragments are usually capable of growing.
The unicorn plant, _Martynia proboscidia_, common in the
southwestern portion of the United States, is sometimes seen in
cultivation. When ripe, the fruit is hard, carrying two stout beaks
with recurved tips. Experiments show it to be admirably adapted to
catch on to the feet of sheep, goats, and cattle, or hold to the fleeces
of the two former.
[Illustration: FIG. 54.--Dry fruit of the unicorn plant adapted to
catching on to the feet of large animals or the wool of sheep.]
44. Water-fowl and muskrats carry seeds in mud.--Seeds and fruits
of aquatic and bog plants that are floating, or in the mud of shallow
water, are often carried by ducks, herons, swallows, muskrats, and
other frequenters of such places, on their feet, beaks, or feathers,
as they hastily leave one place for another. In this way seeds of
water plantain, sedges, grasses, rushes, docks, arrowhead, pondweeds,
duckweed, cat-tail flag, bur reed, bladderwort, water crowfoot, and
many others are transported from one pond, lake, or stream, to another.
In some cases enough of a living plant may be detached and carried
away to keep on growing. Darwin found on the feet of some birds six
and three-quarter ounces of mud, in which were five hundred and
thirty-seven seeds that germinated. Mud may be carried on the feet
of land animals as well as on aquatic animals, not only from ponds
and bogs, but from the fields where seeds may have accumulated in
the earth or washed down the slopes.
45. Why some seeds are sticky.--Some seeds and fruits are sticky;
in some instances the mucilaginous substance is normally moist enough
to adhere to anything that touches it, while in other cases it requires
to be wetted before it will adhere. The seeds of flax, plantain,
peppergrass, basil, sage, dracocephalum, groundsel, drop-seed grass,
and many others less familiar, possess this peculiarity. The berries
of some plants, when fully ripe, burst very easily when touched, and
some of the seeds are then likely to adhere to animals and be carried
away. Some berries of several plants belonging to the nightshade
family have this peculiarity, as well as some of the cucurbits. When
the outer covering of seeds of water lilies, arums, and others are
broken, the gummy secretion is very likely to adhere to the feathers,
or fur, or feet of animals. A number of fruits, and even the upper
fruit-bearing branches, have sticky glands with which to catch on
to any passing object. Among these are some kinds of sedges,
chickweeds, and catchflies.
The sticky substance on seeds and fruits not unfrequently serves
another good turn besides enabling them to adhere to animals. The
slime holds them to the spot where they are to grow, or it enables
some to float or to sink in water, according to the amount of the
mucilage.
46. Three devices of Virginia knotweed.--A perennial plant, four to
five feet high, grows on low land, usually in the shade. It is
_Polygonum Virginicum_, and so far without a common name, unless
Virginia knotweed be satisfactory. It is a near relative of knot grass
and smartweed and Prince's feather. The small flowers are borne on
a long, elastic, and rather stiff stem, and each flower stalk has
a joint just at the base. As this fruit matures, the joint becomes
very easy to separate. It dries with a tension, so that, if touched,
the fruit goes with a snap and a bound for several feet. The shaking
produced by the wind jostling several against each other is
sufficient to send off a number of ripe fruits in every direction.
Like many other plants we have seen, this has more than one way of
scattering seeds, and often more than two ways. Observe the slender,
stiff beak, terminating in two recurved points. Let a person or some
animal pass into a patch of these plants, and at once numerous fruits
catch on wherever there is a chance, and some are shot upon or into
the fleeces of animals, there to find free transportation for
uncertain distances. Should there be a freshet, some of these fruits
will float; or, in case of shallow currents after a rain, some of
them are washed away from the parent plant. Any inquisitive person
cannot fail to be pleased if he experiment with the plant when the
fruit is ripe.
[Illustration: FIG. 55.--Fruit of Virginia knotweed ready to shoot
off when shaken, or to let go of stem and catch on to passing animal.]
47. Hooks rendered harmless till time of need.--There are a number
of rather weedy-looking herbs, common to woods or low land, known
as Avens, _Geum_. They are closely allied to cinquefoil, and all
belong to the rose family. The slender stiles above the seed-like
ovaries of some species of Avens are described as not jointed, but
straight and feathery, well adapted, as we might suppose, to be
scattered by the aid of wind; while others are spoken of as having,
when young, stiles jointed and bent near the middle. In ripening,
the lower part of the stile becomes much longer and stouter. When
a whole bunch of pistils has drawn all the nourishment possible, or
all that is needed, from the plant mother, the upper part of each
stile drops off, leaving a sharp, stiff hook at the end. At this time
each pistil loosens from the torus and can be easily removed,
especially if some animal touch the hooks. To help in holding fast
to animals, there are a number of slender hairs farther down the stile,
which are liable to become more or less entangled in the animal's
hair, fur, wool, or feathers. Even in the small number of plants here
noticed, we have seen that scarcely any two of them agree in the
details of their devices for securing transportation of seeds. I know
of nothing else like the Geum we are now considering. When young and
green, the tip of each hook is securely protected by a knob or bunch,
with a little arm extending above, which effectually prevents the
hook from catching on to anything; but, when the fruit is ripe, the
projecting knob with its little attachment disappears. The figures
make further description unnecessary. To keep the plow from cutting
into the ground while going to or from the field, the farmer often
places a wooden block, or "shoe," over the point and below the plow.
Sometimes we have known persons to place knobs of brass or wood on
the tips of the sharp horns of some of their most active or vicious
cattle, to prevent them from hooking their associates or the persons
having them in charge. Nature furnishes the points of the young fruits
of some species of Avens with knobs, or shoes, for another purpose,
to benefit the plants without reference to the likes or dislikes of
animals.
[Illustration: FIG. 56.--The pistil of Avens in three stages of its
growth.]
48. Diversity of devices in the rose family for seed sowing.--All
botanists now recognize plants as belonging to separate families,
the plants of each family having many points of structure in common.
Among these families of higher plants, over two hundred in number,
is one known as the rose family. Notwithstanding their close
relationship, the modes of seed dispersion are varied. The seeds of
plums and cherries and hawthorns are surrounded by a hard pit, or
stone, which protects the seeds, while animals eat the fleshy portion
of the fruit. When ripe, raspberries leave the dry receptacle and
look like miniature thimbles, while the blackberry is fleshy
throughout. The dry, seed-like fruits of the strawberry are carried
by birds that relish the red, fleshy, juicy apex of the flower stalk.
Each little fruit of some kinds of Avens has a hook at the apex, while
in Agrimony many hooks grow on the outside of the calyx and aid in
carrying the two or three seeds within. Plants of some other families
illustrate the great diversity of modes of dispersion as well as the
roses.
49. Grouse, fox, and dog carry burs.--To the feathers of a ruffed
grouse killed in the molting stage, early in September, were attached
fifty or more nutlets of _Echinospermum Virginicum_ Lehm.
A student tells of a tame fox kept near his home, on the tail of which
were large numbers of sand burs, and a smaller number on his legs
and feet. Another student has seen dogs so annoyed by these burs on
their feet that they gave up all attempts to walk.
Many wild animals unwillingly carry about such fruits, and after a
while most of them remove what they can with claws, hoof, or teeth.
Many of these plants have no familiar common names, but who has not
heard of some of these? enchanter's nightshade, bedstraw, wild
liquorice, hound's tongue, beggar-ticks, beggar's lice,
stick-tights, pitchforks, tick-trefoil, bush clover, motherwort,
sand bur, burdock, cocklebur, sanicle, Avens, Agrimony, carrot,
horse nettle, buffalo bur, Russian thistle. Besides these, a very
large number of small seeds and fruits are rubbed off and carried
away by animals. Some of these stick by means of the pappus, as, for
instance, the dandelion, thistle, prickly lettuce; others by means
of hairs on the seed, such as those of the willow-herb and milkweeds
and willows; or by hairs on the fruit, as virgin's bower, anemone,
cotton grass, and cat-tail flag. These last named are apparently
designed to be wafted by the wind, but they are ever ready to improve
any other opportunity offered, whether it be by water or by clinging
to passing animals.
[Illustration: FIG. 57.--Whole ripe fruit of the common carrot.]
[Illustration: FIG. 58.--Nutlet of stickseed, _Echinospermum_.]
[Illustration: FIG. 59.--Fruit of pitchforks, _Bidens_, with two
barbed points.]
[Illustration: FIG. 60.--A fruit of tick-trefoil, _Desmodium_, and
a few of the grappling hooks enlarged.]
[Illustration: FIG. 61.--A head of the fruits of burdock.]
[Illustration: FIG. 62.--Fruit of cocklebur.]
50. Seeds enough and to spare.--In producing seeds nature is generous,
often lavish. Most seeds are eaten by animals, or fall in places where
they cannot germinate and produce plants, or fall in such numbers
that most of them in growing are crowded and starved to death. A very
small proportion fall on good ground, and succeed in becoming
fruiting plants. A large plant of purslane produces one million two
hundred and fifty thousand seeds; a patch of daisy fleabane, three
thousand seeds to each square inch of space covered by a plant. The
genuine student will not be satisfied till he has selected several
different kinds of plants and counted, or estimated, the number of
seeds produced by each, or the number of seeds furnished to the area
covered by one or by several plants.