Seed Dispersal Part 4

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 quant.i.ty 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 woodp.e.c.k.e.rs, blue jays, and crows; also beechnuts by these birds, and by nuthatches, and by pigeons, before the latter became nearly extinct. Woodp.e.c.k.e.rs 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 pa.s.sing 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, t.i.tmouse, 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 pa.s.sing through the turkey, hen, pigeon, crossbill, bullfinch, goldfinch, nutcracker, t.i.tmouse, and the duck. Ravens and jackdaws pa.s.sed without injury seeds of stone fruits and others with very hard coats. Of seeds that pa.s.sed 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 pa.s.ses through the intestines.]

40. Color, odor, and pleasant taste of fruits are advertis.e.m.e.nts.--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 advertis.e.m.e.nts 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.

[Ill.u.s.tration: FIG. 50.--Raspberry, ripened, picked, and ready to be eaten.]

Sparrows, finches, and similar birds in the winter eat and destroy seeds of gra.s.ses 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 woodp.e.c.k.e.r, 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 woodp.e.c.k.e.r 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 woodp.e.c.k.e.rs named above, also hackberry, black alder, green brier, bayberries.

A number of other woodp.e.c.k.e.rs 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 ill.u.s.trations 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 sa.s.safras, though the flowering dogwood has red leaves as well as red berries.

There is a reason for p.r.i.c.kles 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 p.r.i.c.kles 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 ma.s.s 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 b.a.l.l.s, sticks, eggsh.e.l.ls, 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 ill.u.s.tration, and germinate more promptly than those untouched by birds.

[Ill.u.s.tration: 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 const.i.tute one of the chief sources of their supply of sweet. They build roads and houses, and enjoy society after their fas.h.i.+on. 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, p.r.i.c.kly poppy, dutchman's breeches, squirrel-corn, several species of Corydalis, Seneca snakeroot, and other species of milkworts.

[Ill.u.s.tration: 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.]

[Ill.u.s.tration: 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.

[Ill.u.s.tration: 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, gra.s.ses, 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 acc.u.mulated 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, peppergra.s.s, basil, sage, dracocephalum, groundsel, drop-seed gra.s.s, 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 pa.s.sing 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 Virginic.u.m_, and so far without a common name, unless Virginia knotweed be satisfactory. It is a near relative of knot gra.s.s 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 pa.s.s 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.

[Ill.u.s.tration: FIG. 55.--Fruit of Virginia knotweed ready to shoot off when shaken, or to let go of stem and catch on to pa.s.sing 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 k.n.o.b 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 k.n.o.b 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 k.n.o.bs of bra.s.s or wood on the tips of the sharp horns of some of their most active or vicious cattle, to prevent them from hooking their a.s.sociates or the persons having them in charge. Nature furnishes the points of the young fruits of some species of Avens with k.n.o.bs, or shoes, for another purpose, to benefit the plants without reference to the likes or dislikes of animals.

[Ill.u.s.tration: 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 relations.h.i.+p, 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 ill.u.s.trate 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 Virginic.u.m_ 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, c.o.c.klebur, 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, p.r.i.c.kly 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 gra.s.s, 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 pa.s.sing animals.

[Ill.u.s.tration: FIG. 57.--Whole ripe fruit of the common carrot.]

[Ill.u.s.tration: FIG. 58.--Nutlet of stickseed, _Echinospermum_.]

[Ill.u.s.tration: FIG. 59.--Fruit of pitchforks, _Bidens_, with two barbed points.]

[Ill.u.s.tration: FIG. 60.--A fruit of tick-trefoil, _Desmodium_, and a few of the grappling hooks enlarged.]

[Ill.u.s.tration: FIG. 61.--A head of the fruits of burdock.]

[Ill.u.s.tration: FIG. 62.--Fruit of c.o.c.klebur.]