CHAPTER V.. Seeds Transported by Wind.

SEEDS TRANSPORTED BY WIND.

17. How pigweeds get about.--In winter we often see dead tops of lamb's-quarters and amaranths--the smooth and the prickly pigweeds--still standing where they grew in the summer. These are favorite feeding grounds for several kinds of small birds, especially when snow covers the ground.

Many of the seeds, while still enclosed in the thin, dry calyx, and these clustered on short branches, drop to the snow and are carried off by the wind. Notwithstanding the provision made for spreading the seeds by the aid of birds and the wind, the calyx around each shiny seed enables it to float also; when freed from the calyx, it drops at once to the bottom. Many kinds of dry fruits and seeds in one way or another find their way during winter to the surface of the ice-covered rivers. When the rivers break up, the seeds are carried down stream, and perhaps left to grow on dry land after the water has retired. Most of the commonest plants, the seeds of which are usually transported by water, are insignificant in appearance and without common names, or with names that are not well understood. This is one reason for omitting the description of others which are ingeniously fitted in a great variety of different ways for traveling by water.

18. Tumbleweeds.--Incidentally, the foregoing pages contain some account of seeds and fruits that are carried by the aid of wind, in connection with their distribution by other methods; but there are good reasons for giving other examples of seeds carried by the wind. There is a very common weed found on waste ground and also in fields and gardens, which on good soil, with plenty of room and light, grows much in the shape of a globe with a diameter of two to three feet. It is called Amaranthus albus in the books, and is one of the most prominent of our tumbleweeds. It does not start in the spring from seed till the weather becomes pretty warm. The leaves are small and slender, the flowers very small, with no display, and surrounded by little rigid, sharp-pointed bracts. When ripe in autumn, the dry, incurved branches are quite stiff; the main stem near the ground easily snaps off and leaves the light ball at the mercy of the winds. Such a plant is especially at home on prairies or cleared fields, where there are few large obstructions and where the wind has free access.

The mother plant, now dead, toiled busily during the heat of summer and produced thousands of little seeds. The best portion of her substance went to produce these seeds, giving each a portion of rich food for a start in life and wrapping each in a glossy black coat. Now she is ready to sacrifice the rest of her body to be tumbled about, broken in pieces, and scattered in every direction for the good of her precious progeny, most of whom will find new places, where they will stand a chance the next summer to grow into plants. Sometimes the winds are not severe enough or long enough continued, and these old skeletons are rolled into ditches, piled so high in great rows or masses against fences that some are rolled over the rest and pass on beyond. Occasionally some lodge in the tops of low trees, and many are entangled by straggling bushes. In a day or two, or in a week, or a month, the shifting wind may once more start these wrecks in other directions, to be broken up and scatter seeds along their pathway.

During the Middle Ages in southern Egypt and Arabia, and eastward, a small plant, with most of the peculiarities of our tumbleweed just described, was often seen, and was thought to be a great wonder. It was called the "rose of Jericho," though it is not a rose at all, but a first cousin to the mustard, and only a small affair at that, scarcely as large as a cabbage head. A number of other plants of this habit are well known on dry plains in various parts of the world; one of the most prominent in the northern United States is called the Russian thistle, which was introduced from Russia with flaxseed. In Dakota, often two, three, or more grow into a community, making when dry and mature a stiff ball two to three feet or more in diameter.

One of our peppergrasses, Lepidium intermedium, sometimes attains the size and shape of a bushel basket; when ripe, it is blown about, sowing seeds wherever it goes. The plants of the evening primrose sometimes do likewise, also a spurge, Euphorbia [Preslii] nutans, a weed a foot to a foot and a half high.

Low hop clover, an annual with yellow flowers, which has been naturalized from Europe, has developed recently on strong clay land into a tumbleweed six inches in diameter. The tops of old witch grass, Panicum capillare, and hair grass, Agrostis hyemalis, become very brittle when ripe, and snap from the parent stem and tumble about singly or in masses, scattering seeds by the millions. I have seen piles of these thin tops larger than a load of hay where they had blown against a grove of trees, and in some cases many were caught in the tops of low trees.

Bug seed and buffalo bur are tumbleweeds. In autumn the careful observer with an eye to this subject will be rewarded by finding many other plants that behave more or less as tumbleweeds. Especially is this the case on prairies. These are annuals, and perish at the close of the growing season. There are numerous other devices by which seeds and fruit secure transportation by the wind.

19. Thin, dry pods, twisted and bent, drift on the snow.--The common locust tree, Robinia Pseudacacia, blossoms and produces large numbers of thin, flat pods, which remain of a dull color even when the seeds are ripe. The pods of the locust may wait and wait, holding fast for a long time, but nothing comes to eat them. They become dry and slowly split apart, each half of the pod usually carrying every other seed. Some of the pods with the seeds still attached are torn off by the wind and fall to the ground sooner or later, according to the force of the wind. Each half-pod as it comes off is slightly bent and twisted, and might be considered a "want-advertisement" given to the wind: "Here I am, thin, dry, light and elastic, twisted and bent already; give me a lift to bear these precious seeds up the hill, into the valley, or over the plain."

And the wind is sure to come along, a slight breeze to-day tossing the half-pod a few feet, leaving it perhaps to be again and again moved farther forward. The writer has seen these half-pods transported by this means more than a block. But many of the pods stick to the limbs till winter comes. Then a breeze tears off a few pods and they fall on the snow, which has filled up all the crevices in the grass and between the dead leaves and rubbish. Each half-pod, freighted with every other seed, is admirably constructed; like an ice boat, it has a sail always spread to the breeze. In this way there is often nothing to hinder some of the seeds from going a mile or two in a few minutes, now and then striking some object which jars off a seed or two. The seeds are very hard, and no doubt purposely so, that they may not be eaten by insects or birds; but once in moist soil, the covering slowly swells and decays, allowing the young plant to escape. Thus the locust seeds are provided with neither legs, wings, fins, nor do they advertise by brilliant hue and sweet pulp; but they travel in a way of their own, which is literally on the wings of the wind.

20. Seeds found in melting snowdrifts.--It will interest the student of nature to collect a variety of seeds and dry fruits, such as can be found still on the trees and other plants in winter, and try some of them when there is snow on the ground and the wind blows, to see how they behave. Again, when the first snow banks of the early winter are nearly gone, let him collect and melt a quantity of snow and search for seeds. By this means he can see, as he never saw before, how one neighbor suffers from the carelessness of another.

21. Nuts of the basswood carried on the snow.--Here are some notes concerning the distribution of the spherical nuts of basswood. The small clusters of fruit project from a queer bract which remains attached before and after falling from the tree.

This bract, when dead, is bent near the middle and more or less twisted, with the edges curving toward the cluster of nuts. From two to five nuts about the size of peas usually remain attached till winter, or even a few till spring. This bract has attracted a good deal of attention, and for a long time everybody wondered what could be its use. We shall see. The cluster of nuts and the bract hang down, dangling about with the least breath of wind, and rattling on the trees because the enlarged base of the stem has all broken loose excepting two slender, woody threads, which still hold fast. These threads are of different degrees of strength; some break loose after a few hard gales, while others are strong enough to endure many gales, and thus they break off a few at a time. The distance to which the fruit can be carried depends on the form of the bract, the velocity of the wind, and the smoothness of the surface on which the fruit falls. When torn from the tree the twist in the bract enables the wind to keep the cluster rapidly whirling around, and by whirling it is enabled to remain longer suspended in the air and thus increase the chances for a long journey. In throwing some of these from a third-story window, it was found that a bract with no fruit attached would reach the ground sooner than a bract that bore from two to four solid nuts. The empty or unloaded bracts tumble and slide through the air endwise, with nothing to balance them or steady their descent, while the fruit on other bracts holds them with one side to the air, which prolongs their descent. The less a loaded bract whirls, the faster its descent, and the more a bract whirls when the wind blows, the farther it is carried. The bract that is weighted with a load of fruit acts as a kite held back by a string, and when in this position the wind lifts the whole as well as carries it along. Before snow had fallen in 1896, by repeated moves on a well-mowed lawn, fruit and bracts were carried about two hundred feet, while with snow on the ground the distance was almost unlimited, excepting where there were obstructions, such as bushes and fences. When there is a crust on the snow and a good wind, the conditions are almost perfect. Over the snow the wind drives the bracts, which drag along the branch of fruit much as a sail propels a boat. The curving of the edges of the bract toward the fruit enables the wind to catch it all the better, and to lift it more or less from the snow. With changes in the direction of the wind, there is an opportunity for the fruit of a single tree, if not too much crowded by others, to spread in all directions. After watching these maneuvers, no one could doubt the object of the bent bracts of the basswood, and as these vary much in length and width and shape on different trees, it would seem that perhaps nature is still experimenting with a view to finding the most perfect structure for the purpose.

About one hundred and thirty paces west of the house in which I live stand two birch trees. One windy winter day I made some fresh tracks in the snow near my house, and within a few minutes the cavities looked as though some one had sprinkled wheat bran in them, on account of the many birch seeds there accumulated.

Other fruits in winter can be experimented with, such as that of box elder, black ash, birches, tulip tree, buttonwood, ironwood, blue beech, and occasionally a maple.

22. Buttonwood balls.--Nature seems to have no end of devices for sowing seeds to advantage. Here is one which always interests me. The fruit of the buttonwood, or sycamore, which grows along streams, is in the form of balls an inch and a half in diameter. These balls grow on the tops of the highest branches, and hold on into winter or longer. The stems are about two inches long, and soon after drying, through the action of the winds, they become very flexible, each resembling a cluster of tough strings. The slightest breeze moves them, and they bob around against each other and the small branches in an odd sort of way. After so much threshing that they can hold no longer, the little nuts become loosened and begin to drop off a few at a time. Certain birds eat a few and loosen others, which escape. The illustration shows some of these nuts, each supplied with a ring of bristles about the base, which acts as a parachute to permit the wind the easier to carry them for some distance before falling, or to drift them on the surface of the snow or ice.

23. Seeds that tempt the wind by spreading their sails.--On low lands in the cool, temperate climate of Europe, Asia, and North America, is a common plant here known as great willow-herb, a kind of fireweed (Epilobium angustifolium). There are several kinds of fireweeds. This one grows from three to five feet high, and bears pretty pink flowers. In mellow soil the slender rootstocks spread extensively, and each year new sprouts spring up all around, six to eight feet distant. Below each flower ripens a long, slender pod, which splits open from the top into four parts, that slowly curve away from a central column. The apex of each seed is provided with a cluster of white silky hairs nearly half an inch long.

The tips of the hairs stick slightly to the inside of the recurved valves, some hairs to one valve, and often others to the adjacent valve, thus spreading them apart with the seed suspended between. Four rows of the seeds are thus held out at one time. Often not over half, or even a tenth part, of the seeds are well developed, yet the silky hairs are present and float away in clusters, thus helping to buoy those that are heavy. This is a capital scheme, for when the pods are dry and unfurled, they silently indicate to the slightest breath of air that they are ready for a flight, and it doesn't take much to carry them for a long distance. As an active boy delights to venture again and again over thin ice on a shallow pond in the pasture, half fearing, yet half hoping, that he may become a hero by breaking through and escaping, so likewise many of these seeds and seed-like fruits spread themselves out, as if to tempt the wind to come along and attack them.

The twin fruits of the parsnip and some of its near relatives are light and thin and split apart, each holding on lightly to the top of a slender stem. In this position they are sure to be torn off sooner or later. Somewhat after the manner of the willow-herb behave the pods and seeds of willows, poplars, milkweeds, Indian hemp, and cotton.

24. Why are some seeds so small?--Do you know why so many kinds of plants produce very small and light seeds? Would it not be better if they produced fewer and larger seeds, which would then be stronger and better able to grow under adverse conditions? But a large number of small seeds cost the plant no more effort than a small number of large ones, and the lighter and smaller the seeds and the more there are of them, the better their chances for distribution, especially for long distances. The minute size of spores of most of the fungi are given as reasons why so many of them are so widely distributed.

Why is a boy or man of light weight chosen to ride the horse on the race track? That the animal may have less weight to carry and thereby use his surplus strength in making better time. The less weight the parachute of the seed of the willow-herb has to carry, the greater the chances for success in making a long journey. Of the willow-herb it takes one hundred seeds to weigh a milligram, including the hairs attached to them, and it would take thirty thousand to weigh as much as an ordinary white bean.

25. Seeds with parachutes.--Many years ago large portions of Huron and Sanilac counties of eastern Michigan were swept by a fire so severe that the timber was all killed. Fifteen years later the woody growth consisted mostly of willows, poplars, and birches. The seeds of all kinds of willows and poplars are very light, and are produced in immense quantities. Like those of the great willow-herb, they are beautifully constructed for making long journeys through the air--a fact that explains the frequency of these trees in burned districts. A considerable number of seeds and fruits grow with a parachute attached at one end, not to prevent injury by falling from the tree top, but to enable the wind to sustain and transport them for a longer distance.

26. A study of the dandelion.--In spring the dandelion is almost everywhere to be found; every one knows it--the child to admire, the gardener to despise. From each cluster of leaves spreading flat in the grass come forth several hollow stems, short or tall, depending on the amount of sunshine and shade. Each stem bears, not one flower, but a hundred or more small ones. Around and beneath each yellow cluster are two rows of thin, green, smooth scales (involucre).

The short outer row soon curls back, as though for rest or ornament, or for watching the progress of the colony above; but the inner row has a very important duty yet to perform in guarding the large family within. At night, or in daytime, if the day be wet, the long scales press like a blanket closely about the flowers, and do not permit them to come out; but when the sun is bright, it shrinks the outer side of these scales, which then curl apart, leaving the yellow flowers ready for bees to visit or boys to admire and study. For several days the flowers of a head blossom in succession, each night to be snugly wrapped by the scales, and the next day to be again left open, if the weather be fine. After each flower in turn has been allowed to see the light, and after all have been crawled over by bee and wasp to distribute the yellow pollen that seeds may be produced, there is nothing else to do but patiently wait for a week or two while receiving food from the mother plant to perfect each little fruit and seed. During all this period of maturing, day and night, rain or shine, the scales hold the cluster closely; the stem bends over to one side, and the rain and dew is kept from entering. After a while, on some bright morning, the dandelion stalk is seen standing erect again, and is probably surrounded by many others in a similar position. The dry air shrinks the outside of the scales, and they turn downward; the circle of feathers at the top of the slender support attached to the seed-like fruit below spreads out, and the community, which now looks like a white ball of down, is ready for a breeze. The feathery top is now ready to act as a parachute, and invites the wind to catch up the whole and float it away. If there is no breeze, the moist air of night closes the outer scales; each of the feathery tips closes, and all are secure till the next bright day.

Of a like nature are fruits of thistles, fireweed, prickly lettuce, sow thistles, scabiosa, valerian, cat-tail flag, cotton grass, some anemones, smoke tree, virgin's bower, and some of the grasses.

27. How the lily sows its seeds.--Ripened pods of lilies usually stand straight up on a stiff, elastic stem; beginning at the top, each one slowly splits into three parts, which gradually separate from each other. Why do they not burst open all of a sudden, like pea pods, and shoot the seeds all about and have the job done with? Or why does not the pod burst open at the lower end first, instead of the upper?

Observe that the three opening cells are lashed together loosely with a latticework. No slight breeze can dislodge the seeds, but just see how they behave in a good gale! The elastic stems are swayed back and forth against each other, and some of the upper seeds are tossed out by the wind that passes through the lattice, and at such times are often carried to some distance. The seeds at the top having escaped, the dry pods split down farther and still farther and open still wider, till the bottom is reached. As the seeds are not all carried away the first or even the second time, and as succeeding breezes may come from different directions, it is thus possible for the lily to scatter its seeds in all directions.

The seeds of the lily are flat, very thin, and rather light, not designed to be shot out like bullets, but to be carried a little way by the wind; the pods are erect, and open at the top, that the seeds need not escape when there is no wind or unless some animal gives the stem a strong shake. The latticework was made for a purpose, and the gradual opening of the pods prevents the supply from all going in one direction or in one day, for a better day may arrive. The student will look for and compare the following: Iris, figwort, wild yam, catalpa, trumpet-creeper, centauria, mulleins, foxglove, beardtongue, and many other fruits.

28. Large pods with small seeds to escape from small holes.--The large ripe pod of the poppy stands erect on a stiff stem, with a number of small openings near the top. The seeds are nearly spherical, and escape, a few at a time, when the stem is shaken by the wind or some animal, thus holding a reserve for a change of conditions. Here is an illustration of ripe pods of a bellflower, Campanula turbinata, nodding instead of erect.

The small holes are still uppermost, but to be uppermost in this case it is necessary for them to be at the base of the pod.

29. Seeds kept dry by an umbrella growing over them.--When mature, the apple of Peru, Nicandra, keeps every dry bursting fruit covered with a hood, umbrella, or shed, so that seeds may be kept continually dry and may be spread with every shake by the wind, or by an animal, in rainy weather as well as in dry.

In the words of Dr. Gray, "The fruit is a globular dry berry, enclosed by a five-parted, bladdery inflated calyx." The margins of the lobes of the calyx curl upwards and outwards as the berry hangs with the apex downward.

The berry is as large as one's thumb, and when ripe, bursts open irregularly on the upper side as it hangs up under the calyx. As the covering of the pod opens more and more, a few seeds at a time may be rattled out by wind or animal. The numerous large and light fruits, with calyx surrounding them, are each supported on a nodding stem, stiff and elastic, which gives the wind a good chance to sway them about. Water does not seem to get into the berries even when they are torn open, for when it is poured over the branches it rolls off the calyx roof as freely as from a duck's back. The fruits of Physalis are apparently kept dry in a manner similar to the apple of Peru, although when first mature they are soft and juicy, considerably like a ripe tomato.

30. Shot off by wind or animal.--The calyx of sage, bergamot, and most other mints, remains dry and stiff, as a cup to hold one to four little round nutlets as they ripen. The figure shows two of these in section, as they are attached to the main stem of the plant, or one of its branches. Observe the direction taken by the upper and by the lower points of the calyx. When dry, the plant behaves somewhat as follows: when the wind jostles the branches against each other, or when an animal of some kind hits the plant, this movement causes many of these cups to get caught; but the elastic stem comes suddenly back to its place, and in so doing flips a nutlet or more from its mouth one to six feet, somewhat as a boy would flip a pea with a pea-shooter. In our garden, July 2, when plants of sage, Salvia interrupta, were ripening their fruit, we found it difficult to collect any seeds, but seedlings were observed in abundance on every side of the plant, some to the distance of six feet. Plants dispersing seeds in this manner have been called catapult fruits. Examine ripening fruits of blue curls, pennyroyal, germander, balm, horehound, dittany, hyssop, basil, marjoram, thyme, savory, catmint, skullcap, self-heal, dragon's head, motherwort, and various dry fruits of several chickweeds.

31. Seed-like fruits moved about by twisting awns.--Most of the grains of grasses are invested with glumes, or chaff, and a considerable per cent of the chaff has awns, some of which are well developed and some poorly developed. The distribution of such grasses depends on several agents--wind, water, and animals. The chaff and awns of all are hygroscopic; that is, are changed by differences caused by variation of moisture in the air. Sweet vernal grass, tall oat grass, holy grass, redtop, animated or wild oats, blue-joint, and porcupine grass are among them. When mature, the grain and glumes drop off, or are pushed off, and go to the ground. When moist, these awns untwist and straighten out, but when dry they coil up again; with each change they seem to crawl about on the ground and work down to low places or get into all sorts of cracks and crevices, where the first rain is likely to cover them more or less with earth, after which they are ready for growth.

32. Grains that bore into sheep or dogs or the sand.--Porcupine grass, Stipa spartea, grows in dry soil in the northern states, but more particularly on the dry prairies of the central portion of the United States. This grass, when ripe, has a very bad reputation among ranchmen for the annoyance the bearded grain causes them. The grains are blown into the stubble among grasses with the bearded point down, sticking into the soil. The first rain or heavy dew straightens out the awns, which are twisted again as they dry. The bearded point works a little farther with each change, and after twisting and untwisting a number of times it gets down three or four inches into the sand, often to moisture, where the awns decay and the grain germinates. Here is an admirable scheme for moving about and for boring into the ground. But this is not all. The grains are quick to catch fast to clothing, as people move among the plants, and they are admirably fitted for attaching themselves to dogs and sheep, which they annoy very much. These animals transport the grains for long distances. The twisting and untwisting of the awns enable the grain to bore through the fleeces, and even to penetrate the skins and make wounds which sometimes cause the death of the animal. Examine also seeds of pin clover, Alfilerilla, which is becoming abundant in many parts of the world.

33. Winged fruits and seeds fall with a whirl.--The large fruit of the silver maple falls in summer. As these trees are most abundant along the margins of streams, the fruit often drops into the water and is carried down stream to some sand drift or into the mud, where more sand is likely to cover them. Thus sown and planted and watered, they soon grow and new trees spring up. But in many instances a strong breeze, sometimes a whirlwind, has been seen to carry these mature fruits from the tree to a distance of thirty rods.

A thin sheet of paper descends more slowly than the same material put in the form of a ball. On the same principle, many seeds and fruits are flattened, apparently for a purpose; not that they may be easily shot through the air by some elastic force, not to increase their chances for attachment to animals, but to enable the wind to sustain them the longer and carry them farther. Some seeds and dry fruits are said to have wings, with the general understanding that they are by this means better fitted to be sustained in air. We shall find that all or nearly all flattened seeds and dry fruits, also winged seeds and fruits, are one-sided, unbalanced, and more or less twisted; consequently, in falling to the ground they whirl about, and are thus kept much longer in the air than they would be if shaped more like a winged arrow. Even the wings on the fruit of some of the ashes are twisted, though many of them are flat. Experiments with these things are sure to interest inquisitive children, or even older persons, when once started right; they are likely to prove as interesting as flying kites, skating, fishing, or coasting on the hillside. Try experiments with seeds of catalpa, trumpet-creeper, wild yam, pine, spruce, arbor vitae, and fruits of maple, box elder, birch, hop tree, blue beech, ailanthus, ash, tulip tree,--in fact, anything of this nature you can find, whether the name is familiar or not. No two of them will behave in all respects alike.

34. Plants which preserve a portion of their seeds for an emergency.--Many a great general or business man has learned by experience and observation that it is usually unwise to exhaust all resources in one effort. If possible, he always plans to have something in reserve for an emergency--a loophole for escape from difficulty. We have seen in many instances that plants are endowed with the same trait. This is well illustrated by the way in which the jack-pine, Pinus [Banksiana] divaricata, holds in reserve a portion of its seeds, to be used in case the parent trees are killed by fire. In 1888 I made a study of this tree as it lives on the sandy plains of Michigan. The tree is often killed by fire, and never sprouts from the stump, as do oaks, willows, cherries, and most other trees. The jack-pine grows readily and rapidly from seed dropped on the sand, and begins to bear cones and seeds in abundance while it is yet only a few years old, perhaps as young as five years in some instances. The cones open slowly to liberate their seeds, some of them only after months or even years, and in some cases they never open at all. I have seen cones containing good seeds that had been nearly grown over by the tree. Dry weather, the dryer and hotter the better, causes many of these stubborn old cones to open their scales and allow the seeds to escape. What can be the advantage in cones of this nature? Let us see. A brisk fire passes over the ground at irregular intervals, usually of from one to ten years; it licks up all dry leaves and sticks, and kills the pine trees and all else above ground. The soil and the trunks of trees are blackened, and by lack of reflection the heat of the sun is rendered more intense; besides, the heat of the fire acts slowly on the unburned cones as they are left on the dead trees. By the time the quick hot fire has passed over, the cones have slowly opened and begun scattering seeds on the vacant and newly burned ground, at a time when there is the best possible chance for them to grow. I picked a few unopened cones which, according to my judgment, were from two to four years old. They were placed under glass in a dark sheet-iron dish and exposed to the sun. The extra heat caused the cones to open; many seeds were obtained and sown, and in five days they began to come up, 95 per cent germinating. From the same tree I selected at the same time older cones, which I believe to be from four to six years old at least. From these, 225 seeds were sown, 191 of which germinated--about 85 per cent.