CHAPTER III
PLANTS MULTIPLY BY MEANS OF STEMS
7. Two grasses in fierce contention. —In growing a lawn at the Michigan Agricultural College, a little Bermuda grass was scattered with June grass, and the struggle has been most interesting. In the spring and for six weeks in autumn, when moisture usually abounds and the weather is cool, June grass thrives and little else is seen. In the dry, hot weeks of July and August, June grass rests and the Bermuda, which continues to spread, assumes control of the lawn, with but little of the June grass in sight. Each struggles for possession and does the best it can, and to some extent one supplements the other, with the result that at all times from spring to fall there is a close mat of living green which delights the eye and is pleasant to the feet that tread upon it. In soft ground, with plenty of room, a bit of quick or quack grass, or Bermuda, will extend in a year three to five feet or more in one direction.
June grass, quick grass, Bermuda grass, redtop, and white clover, wherever opportunity offers, spread by means of jointed stems, creeping and rooting at every joint on the surface of the ground or a little way below. These are not roots at all, but true stems somewhat in disguise. Here may also be mentioned, as having similar habit, artichokes, peppermint, spearmint, barberry, Indian hemp, bindweed, toadflax, matrimony vine, bugle-weed, ostrich fern, eagle fern, sensitive fern, coltsfoot, St. John'swort, sorrel, great willow-herb, and many more.
8. Runners establish new colonies. —The spreading of strawberries by runners must be familiar to every observer. In 1894 a student reported that a wild strawberry plant in the botanic garden had produced in that year 1230 plants. Weeds were all kept away, the season was favorable, the soil sandy; but on one side, within a foot and a half, progress was checked by the presence of a large plant of another kind. The multiplication of this plant by seeds, in addition to that by runners, would have covered a still greater area of land. Other plants with runners much like the strawberry are: several kinds of crowfoot, barren strawberry, cinquefoil, strawberry geranium, and orange hawkweed. Plants of the star cucumber, one-seeded cucumber, grapes, morning-glories, and others, spread more or less over bushes or over the ground, and are thus enabled to scatter seeds in every direction.
9. Branches lean over and root in the soil. —A black raspberry grows fast in the ground and has to stay in one spot for life. It has neither legs, feet, nor wings, and yet it can travel. The bush takes deep root and spreads out its branches, which are sometimes ten feet or more in length; the tips of these branches curve over to the ground six feet away, and finally take root; from these roots new colonies are formed, five to twenty in a year from one bush.
True, the old roots do not get far, and the new plants only get about six feet in one season, but they have made some progress. This is rather slow locomotion, you say; but let us look a little farther, remembering that a seed is a little plant packed ready for transportation. This second mode of spreading will be described on a future page.
10. Living branches snap off and are carried by water or wind. —Some trees and shrubs among the willows are called snap-willows, because their branches are very brittle; on the least strain from wind, rain, sleet, or snow, the smaller branches snap off near the larger branches or the main trunk, and fall to the ground. At first thought this brittleness of the wood might seem to be a serious defect in the structure of the tree or shrub, although they seem to produce branches enough for their own use.
But the branches which are strewn all around after a storm often take root in the low ground where they fall; some of them are carried down stream by the current, and, lodging on the shore below, produce new trees or bushes. During the winter of 1895 and 1896 a group of seven white willows, near a brook on the campus of the Michigan Agricultural College, was at one time loaded with sleet. There was considerable snow on the ground, which, of course, was covered with an icy crust. In a little while the sleet melted from the fallen branches strewn about, and a moderate breeze then drifted the smallest of the twigs in considerable numbers over the icy snow. Some of these were found thirty rods distant from the parent trees – not down stream in the valley of the brook, but up the stream. Had not the low ground been covered with a dense growth of grass, some of these branches might have started new trees where the wind had left them.1
The branches on slow-growing limbs of cottonwood and large-toothed aspen are much enlarged at the nodes, and at these places are brittle, often separating from the tree and breaking up into pieces. Under a small cottonwood were picked up a bushel or more of such limbs, all yet alive. These trees are common on low land, and, like snap-willows, the severed twigs may find a chance to grow on moist soil.2
In a greenhouse a potted plant of Selaginella emiliana(?) was placed on the bench near the aisle, where it was often brushed by people in passing. Small branches, not being firmly attached, were frequently broken from the main plant and fell upon the moist sand, where they rooted in abundance.
CHAPTER IV
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.