Chapter Ix. the Response of the Plant to Its Surroundings

I. ECOLOGICAL FACTORS

MATERIAL.—A number of small flowerpots filled with soils of as many different kinds as can be found in the neighborhood.

=308. Definition.=—By ecology is meant the relation of plants to their surroundings, which may be considered under three general heads: their relations to inanimate nature, to other plants, and to animals. The subject has been touched upon repeatedly in the foregoing pages, and, in fact, it is impossible to treat of any branch of botany without some reference to it. All that was said about the adjustment of leaves for light and moisture, and their adaptations for protection and food storage, about the devices for pollination, and for fruit and seed dispersal, really belong to ecology.

=309. Symbiosis.=—The relations of plants to animate nature are biological factors, and may act in two ways: (1) through the destruction of vegetation by hungry animals and by parasitic and disease-producing organisms; and (2) by associations for mutual benefit, such as are described in section viii of chapter VII. Associations of this kind are included under the general term symbiosis, a word which means “living together.” In its broadest sense symbiosis refers to any sort of dependence or intimate organic relation between different kinds of individuals, and so may include the climbing and parasitic habits; but it is usually restricted to cases where the relation is one of mutual benefit. It may exist either between plants of one kind with those of another, between animals with animals, or between plants and animals, as in the case of the clover and bumblebee, and the yucca and pronuba.

The occurrence of root tubercles on certain of the leguminosæ (63) is a clear case of symbiosis, the microscopic organisms in the tubercles getting their food from the plant and at the same time enabling it to get food for itself from the air in a way that it could not otherwise do.

=310. Relations with inanimate nature.=—But it is to the relations of plants with inanimate nature, and their grouping into societies under the influence of such conditions, that the term “ecology” is more strictly applied. The external conditions that lead to the grouping are called ecological factors. The most important of these are temperature, moisture, soil, light, and air, including the direction and character of the prevailing winds. Each of these factors is complicated with the others and with conditions of its own in a way that often makes it difficult to determine just what effect any one of them may have in the formation of a given plant society.

=311. Temperature= may be even and steady, like that of most oceanic regions, or it may be subject to sudden caprices and variations, like the “heated terms” and “cold snaps” that afflict our Eastern coast region every few years. It is not the average temperature of a climate, but its extremes, especially of cold, that limit the character of vegetation.

Temperature probably has more influence than any other factor upon the distribution of plants over the globe; but it can have little or no effect in evolving local differences in vegetation, because the temperature of any given locality, except on the sides of high mountains, will ordinarily be the same within a circuit of many miles.

=312. Moisture=, again, may be of all degrees, from the superabundance of lakes and rivers and standing swamps, to the arid dryness of the desert, and the water may be still and sluggish, or in rapid motion. It may exist more or less permanently in the atmosphere, as in moist climates like those of England and Ireland, where vegetation is characterized by great verdure; or it may come irregularly in the form of sudden floods, or at fixed intervals, causing an alternation of wet and dry seasons. Moreover, the moisture of the soil or the atmosphere may be impregnated with minerals or gases, which may affect the vegetation independently of the actual amount of water absorbed.

Snow is a form of water which may act in two entirely opposite ways: (1) by keeping the atmospheric precipitation locked up in a solid state and thus bringing about a condition analogous to drought—for example, in arctic deserts and Alpine snow fields; (2) by causing annual floods and overflows when it melts in the spring, as in the Nile and Mississippi valleys.

In cold temperate regions it also influences vegetation to a considerable extent by covering the warm earth like a blanket during winter, and thus protecting tender seeds and shoots that otherwise would not be able to survive.

=313. Light= may be of all degrees of intensity, from the blazing sun of the treeless plain to the darkness of caves and cellars where no green thing can exist. Between these extremes are numberless intermediate stages: the dark ravines on the northern side of mountains, the dense shade of beech and hemlock forests, and the light, lacy shadows of the pines,—each characterized by its peculiar form of vegetation. Absence of light, too, is usually accompanied by a lowering of temperature and a reduction of transpiration, factors which tend to accentuate the difference between sun plants and shade plants, giving to the latter some of the characteristics of aquatic vegetation. Generally, the tissues of these are thin and delicate, and having no need to guard against excessive transpiration, they wither rapidly when cut or exposed to too great intensity of heat and light.

=314. Winds= affect vegetation, not only as to the manner of seed distribution and the conveyance of pollen, but directly by increasing transpiration, and necessitating the development of strong holdfasts in plants growing upon mountain sides and in other exposed situations. The nature of the region from which they blow—whether moist, dry, hot, cold, etc.—is also an important factor. In a district open to sea breezes, live oaks, which require a salt atmosphere, may sometimes be found as far as a hundred miles from the coast.

=315. Soil.=—While water is the most important, soil is perhaps the most interesting of these factors to the farmer, because it is the one that he has it most largely in his power to modify. It is to be viewed under two aspects: first, as to its mechanical properties, whether soft, hard, compact, porous, light, heavy, etc.; secondly, as to its chemical composition and the amount of plant food-materials contained in it. The first can be regulated by tillage and drainage, the second by a proper use of fertilizers.

EXPERIMENT 92. TO SHOW THE INFLUENCE OF SOIL AS AN ECOLOGICAL FACTOR.—Fill a number of small earthen pots with all the different kinds of soil that are to be found in your neighborhood. Keep well moistened and make a list of the plants that appear spontaneously in each. Is there any difference in the kinds produced by different soils? In vigor or abundance of the same or different kinds? Do more seedlings appear in any of the pots than could live if left alone? What becomes of a majority of the seedlings that come up in a state of nature?

After a time, stop watering until all the plants are dead and new ones cease to appear. Notice the rate at which vegetation dies out in each and the kind of plants that can live longest without water. Which of the different soils is capable of sustaining vegetation longest without a fresh supply of moisture? To what quality of the soil is this due? (Exp. 53.)

Practical Questions

1. Is the relation between man and the plants cultivated by him a symbiosis? (309.)

2. Why is it that plants of the same, or closely related species are found in such different localities as the shores of Lake Superior, the top of Mt. Washington, and the Black Mountains in North Carolina? (311, 330.)

3. Which of the five ecological factors mentioned in paragraphs 311-315 has probably most largely influenced their distribution?

4. What is the prevailing character of the soil in your neighborhood?

5. Is your climate moist or dry? Warm or cold?

6. Can you trace any connection between these factors and the prevailing types of vegetation?

II. PLANT ASSOCIATIONS

MATERIAL.—The subject is not well suited to laboratory work, though, if time permits, it is recommended that a detailed study be made of at least one typical hydrophyte, halophyte, and xerophyte plant. Some good examples are: (1) Hydrophyte: pond weed, waterlily, pipewort (Eriocaulon), bladderwort, arrowhead (Sagittaria); (2) Halophyte: sea lavender, sea rocket, sea lettuce, water hyacinth; (3) Xerophyte: cactus, century plant, pineapple, stonecrop, purslane, lichen.

=316. Modes of grouping.=—Plants group themselves in their favorite habitats, not according to their botanical relationships, but with regard to the predominance of one or more of the ecological factors that influence their growth. Sometimes one or two species will take practical possession of large areas, like the coarse grasses that spread over certain salt marshes, or the pines that formerly constituted the sole forest growth over extensive regions in North Carolina and Maine. Exclusive growths of this kind over limited areas are sometimes called plant colonies, and the individuals composing them belong, as a general thing, to the hardy, pushing sort known as “pioneers,” which are among the first to take possession of new soil and force their way into unoccupied territory. But more usually we find a great diversity of forms brought together by their common requirements as to shade, soil, moisture, and other external conditions.

Any well-defined assemblage of plants, whether of one kind or many, originating in such a common response to the same influences, is called a formation. These associations are variously classed, according to the nature of their habitat, as salt water, fresh water, sand hill, swamp, bog, river bottom, or such other kinds as their ecological character may indicate. Local conditions in limited areas may lead to the segregation of smaller and more compact groups called societies. This term, however, is used rather loosely, being treated in some works as synonymous with formations, in others as analogous with what have here been defined as colonies.

=317. Principles of subdivision.=—The mixed associations described in the last paragraph are quite independent of botanical relationships, and any of the factors named in 310, or others of a different kind, could be made the basis of their classification. They might be grouped, for instance, according to their economic uses, or according to origin, whether native or introduced, as best suited the purpose of the classification in each case. The moisture factor, however, has been generally agreed upon as the one most convenient for ordinary purposes. Upon this principle plants are divided into three great groups:—

=Hydrophytes=, or water plants, those that require abundant moisture.

=Xerophytes=, or drought plants, those that have adapted themselves to desert or arid conditions.

=Mesophytes=, plants that live in conditions intermediate between excessive drought and excessive moisture. To this class belong most of our ordinary cultivated plants and the greater part of the vegetation of the globe.

=Halophytes=, “salt plants,” is a term used to designate a fourth class, based not directly upon the water factor, but upon the presence of a particular mineral in the water or the soil which they can tolerate. They seem to bear a sort of double relation to hydrophytes on the one hand and to zerophytes on the other.

=318. Hydrophyte societies.=—These embrace a number of forms, from those inhabiting swamps and wet moors, to the submerged vegetation of lakes and rivers. An examination of almost any kind of water plant will show some of the physiological effects of unlimited moisture. Take a piece of pondweed, or other immersed plant, out of the water and notice how completely it collapses. This is because, being buoyed up by the water, it has no need to spend its energies in developing woody tissue. Floating and swimming plants will generally be found to have no root system or very small ones, because they absorb their nourishment through all parts of the epidermis directly from the medium in which they live. That they may absorb readily, the tissues are apt to be soft and succulent and the walls of the cells composing them very thin. In some of the pipeworts (Eriocaulon), the ells are so large as to be easily seen with the unaided eye. If you can obtain one of these, examine it with a lens and notice how very thin the walls are. Water plants also contain numerous air cavities, and often develop bladders and floats, as in the common bladderwort and many seaweeds. The leaves of submerged plants are usually either greatly reduced in size or very much cut and divided, while the ones that rise above water, like those of the water lily, are apt to be large and entire, to facilitate floating, and have stomata on their upper surface. Floating plants sometimes form such large colonies as to be a serious menace to navigation. Well-known instances of this are the water hyacinths in the St. John’s River, Florida, and the vast formations of swimming gulfweed from which the Sargasso Sea takes its name.

=319. Swamp societies.=—These include what may be regarded as the amphibious portion of the hydrophyte group. They compose the sedge and cattail bogs, reed jungles, moss and fern thickets, forests of cypress, magnolia, black gum, pine, tamarack, balsam, and the like. The sedges and cattails are the pioneers of these societies, which tend constantly to encroach upon the water and so prepare the way for the advance of other colonists. Drawing their nourishment from the loose soil in which they are anchored, and lacking the support of a liquid medium, they develop roots and vascular stems. The roots of plants growing in swamps have difficulty in obtaining proper aëration on account of the water, which shuts off the air from them; hence they are furnished with large air cavities, and the bases of the stems are often greatly enlarged, as in the Ogeechee lime (Nyssa capitata) and cypress, to give room for the formation of air passages. The peculiar hollow projections known as “cypress knees” are arrangements for aërating the roots of these trees.

=320. Xerophyte societies= are adapted to conditions the reverse of those affected by hydrophytes. The extreme of these conditions is presented by regions of perennial drought, like our Western arid plains and the great deserts of the interior of Asia and Africa. Under these conditions plants have two problems to solve,—to collect all the moisture they can and to keep it as long as they can. Hence, plants of such regions have a diminished evaporating surface, owing to the absence of foliage and the compacting of their tissues into the stem, after the manner of the cactus and prickly euphorbia; or their leaves may become thick and fleshy so as to resist evaporation and retain large amounts of moisture, as in the case of the yucca and century plant. They also frequently develop a thick, hard epidermis, or cover themselves with protective hairs and scales.

The principal types of xerophyte plants are: (1) the lichens, mosses, and saxifrages found on bald rocks and mountain cliffs; (2) sand plants, such as cockspur grass, sand spurry, wiregrass, and the like, inhabiting sea beaches and pine barrens; (3) the sage brush, greasewood, and switch plants of our Western alkali plains; (4) the cactus and yuccas of southern California, Arizona, and Mexico; (5) the acacias, agaves, and hardy “chapparal” thickets of southern Texas and Mexico. The first class are of importance as the pioneers and pathfinders of the xerophyte community. In tropical and polar deserts alike they are the first settlers, and by aiding in the disintegration of rocks and their gradual conversion into soil, they pave the way for the coming of the higher plants, and it may be of man himself.

=321. Partial xerophytes.=—Plants exposed to periodic and occasional droughts frequently provide against hard times by laying up stores of nourishment in bulbs and rootstocks and retiring underground until the stress is over. This is known as the geophilous, or earth-loving, habit. Others, as some of the lichens, and the little resurrection fern (Polypodium incanum, Figs. 419, 420), so common on the trunks of oaks and elms in the Southern States, make no resistance, but wither away completely during dry weather, only to waken again to vigorous life with the first shower.

=322. Physiological xerophytes.=—Plants growing in thin or poor soil, such as that on denuded hillsides, fresh railroad cuts, and newly graded streets, are apt to take on a more or less xerophytic character, even though there may be no lack of moisture. Such soils are called “new” because the mineral elements in them have not been exposed long enough to have become decomposed and mixed with humus, and the vegetation that first populates them has to do the pioneer work of disintegrating and impregnating the substratum with humus. For similar reasons the vegetation of sandy bogs and sea beaches, owing to the poverty of the soil in nitrogenous matter, usually develops xerophyte adaptations, even though there may be a superabundance of moisture. Plants growing on high mountain tops and in cold arctic bogs take on the same characteristics (Fig. 410). Such situations are said to be “physiologically dry,” because the moisture they have is not in a condition to be readily absorbed. The vegetation of arctic regions suffers more from physiological drought than from cold.

=323. Halophytes= include plants growing by the seashore and the vegetation around salt springs and lakes and that of alkali deserts. Seaweeds are in a sense halophytes, since they live in salt water, but as they are true aquatic plants and exhibit many of the peculiarities of hydrophytes in their mechanical structure, they are classed with them. The name halophyte applies more particularly to land plants that have adapted themselves to the presence in the soil or in the atmospheric vapor, of certain minerals, popularly known as salts, which cause them to take on many xerophyte characteristics. The reason for this, as was shown in Exp. 39, is because the mixture of salt in the water of the soil increases its density so that it is difficult for the plant to absorb as much as it needs, and thus halophytes are living under “physiologically” xerophyte conditions. If you have ever spent any time at the seashore, you cannot fail to have observed the thick and fleshy habit exhibited by many of the plants growing there, such as the samphire, sea purslane (Sesuvium), and sea rocket (Cakile). A form of goldenrod found by the seashore has thick, fleshy leaves, and is as hard to dry as some of the fleshy xerophytes.

Another characteristic of desert plants that is common also to seaside vegetation is the frequent occurrence of a thick, hard epidermis, as in the sea lavender and saw grass. The live oaks, trees that love the salt air and never flourish well beyond reach of the sea breezes, have small, thick, hard leaves, very like those of the stunted oaks that grow on the dry hills of California. The presence of spines and hairs, it will be observed, is also very common; e.g. the salsola, the sea oxeye, and the low primrose (Œnothera humifusa). In other cases the leaf blades are so strongly involute or revolute (202) as to make them appear cylindrical. All these, it will be observed, are xerophyte adaptations, and the object in both cases is the same—the conservation of moisture.

=324. Mesophytes.=—These embrace the great body of plants growing under the ordinary conditions of temperate regions, which may vary from the liberal water supply of low meadows and shady forests to the almost desert barrenness of dusty lanes and gullied, treeless hillsides. The forms and conditions they present are so varied that it would be impracticable to consider them all in a work like this, but they may be summed up under the two general heads of (1) open ground and (2) woodland. Under the first are included: (a) all cultivated grounds—fields, meadows, lawns, pastures, and roadsides, with their characteristic shrubs, flowers, and grasses; (b) heaths and plains of northern or alpine regions, with their low, stunted perennials and bright, but fugacious, flowers. Under the second are classed all woods, thickets, and copses, with the shrubs and herbs that form their undergrowth. These may be grouped in three main divisions: (c) mixed forests of maple, ash, oak, hickory, birch, sweet gum, etc.; (d) pure forests of pine, balsam, fir, cypress, and the like; and finally (e), the perennial splendors of the tropical forest, where the vegetation of the globe reaches its climax in luxuriance and variety of growth.

Practical Questions

1. Why do florists cultivate cactus plants in poor soil? (320.)

2. What would be the effect on such a plant of copious watering and fertilizing?

3. Why must an asparagus bed be sprinkled occasionally with salt? (323.)

4. If a gardener wished to develop or increase a fleshy habit in a plant, to what conditions of soil and moisture would he subject it? (320, 323.)

5. What difference do you notice between blackberries and dewberries grown by the water and on a dry hillside?

6. Are there corresponding differences in the root, stem, and leaves of plants growing in the two situations, and if so account for them?

7. When a tract of dry land is permanently overflowed by the building of a dam or levee, why does all the original vegetation die, or take on a sickly appearance? (319.)

8. Should plants with densely hairy leaves be given much water, as a general thing? (202, 320.)

9. A farmer planted a grove of pecan trees on a high, dry hilltop; had he paid much attention to ecology? Give a reason for your answer.

10. Why do the branches of trees often die, or fail to develop, on the windward side? (314.)

11. Why do trees grown in dry soil have harder wood than the same kind grown in wet soil? (123, 318.)

III. ZONES OF VEGETATION

=325. The origin of vegetable zones.=—The terms “zone” and “zonation” are used to express a general tendency of plant societies and formations to distribute themselves in more or less regular belts or strata, relatively to the varying intensity of the prevalent ecological factor of their habitat. In almost every locality there exists some special feature—a pond, a brook, a small ravine, an isolated hilltop, a deserted quarry, a gravel pit, or a railroad cut,—sufficiently distinct from the general surroundings to exercise a perceptible control over the vegetation in its immediate vicinity, and thus to become the starting point of a series of plant zones that mark the decreasing influence of the factor concerned, by their change of character as they recede from its point of greatest intensity. Starting from a barren, exposed hilltop, for example, with a covering of dry broom sedge (Andropogon) and fleabane, we encounter next an almost desert zone of washed and gullied slopes in whose hard, sunbaked soil nothing but a few scrub pines and brambles can gain a foothold. This will, perhaps, be succeeded, by a straggling belt of sassafras, sumac, and buckthorn, mixed with cat brier and blackberry canes, beyond which, at the foot of the hill, begins a stretch of meadow, or a bit of woodland crossed by a brook, or hollowed into a boggy depression. From this new factor originates a second series of zonations, passing through all the stages of bog, swamp, shade, and sun plants, back to the prevailing type of the region. Moisture is really the controlling factor in both cases, its influence in the first being negative,—that is, inversely,—and in the other, positive, or directly proportioned to the quantity present.

=326. Direction of zonation.=—When the direction in which the controlling factor changes is horizontal, as with soil and water, the zonation will be horizontal; when, as in the case of light, it is vertical, the zonation or stratification will be vertical. Examples of this can be observed in the growth of almost any forest area, the natural order of succession being: (1) a ground layer of mosses and fungi; (2) low, creeping vines,—partridge berry, trailing arbutus, twinflower (Linnæa); (3) small ferns and low flowering herbs—pyrola, clintonia, trillium; (4) a zone of tall herbs and low bushes—royal fern, cohosh (Actæa), blueberries; (5) tall herbs and shrubs, small trees, and climbing vines—kalmia, dogwood, farkleberry, smilax, Virginia creeper; (6) tall treetops towering up into full sunlight.

When the physical cause of intensity is a central area, such as a pond or a hilltop, the zonation will be concentric; that is, the different belts will succeed each other in widening circles more or less complete. Where the controlling cause extends in a line, as a river, or a chain of mountains, the zones run in parallel belts on each side of it, and the zonation is bilateral. In any case, however, it is seldom regular, being frequently broken and interrupted through the intervention of other factors. Nor must precisely the same kind of plants be always looked for in similar situations, though their place is usually occupied by kindred species and genera. The common pitch pine, for instance, of the Northern sand barrens is represented in sandy districts farther south by the tall, long-leaved pine, a kindred species.

=327. Succession.=—Zonation is a regular succession of different kinds of plants in space; there is also an analogous succession in time, as, when the vegetation of a locality is killed off by fire or other cause, plants of an entirely different character will nearly always spring up to occupy its place. A forest of pine, for instance, is rarely followed by conifers, but by a growth of hardwood trees, and vice versa—nature thus giving an impressive example as to the effectiveness of a rotation of crops.

Succession may be influenced by a variety of causes. Two of the most efficient are: (1) the exhaustion of the soil by the long-continued growth of one formation (60), thus causing a deficiency of mineral material suited for the support of plants of that kind; (2) the migration of new species into the denuded territory where those which have different requirements as to mineral nutrients from the former inhabitants will, other things being equal, have the best chance to succeed.

=328. Invasion.=—A rapid and widespread occupation of any territory by a new species is called an invasion. Notable examples of invaders are those of the Russian thistle in the northwestern states of the Union, and the “bitterweed” (Helenium tenuifolium) that has almost driven out the hardy dog fennel (Anthemis cotula) which formerly held undisputed possession of arid places throughout the South Atlantic states. A still more remarkable instance is the invasion of the Japanese honeysuckle (Lonicera Japonica), originally introduced for ornament, but which has naturalized itself within the last thirty years and overrun waste places everywhere, from the Gulf to the Potomac, with a vigor and luxuriance equaled by few of our native species. As its beauty and fragrance are even more conspicuous in a state of nature than under cultivation, and as it can, moreover, be made very useful in stopping gullies and washes, its phenomenally rapid occupation of so large a territory has caused no alarm and consequently attracted little attention.

=329. Climatic zones.=—These are more general groupings than those we have been considering. They follow in a rough way the parallels of latitude, and are classed accordingly as: (1) tropical; (2) subtropical; (3) temperate; (4) boreal or (on mountains) subalpine; (5) arctic or (on high mountains) alpine. Taking the cultivated plants of our own country by way of illustration, we have the subtropical zone, embracing Florida and the southern portion of the Gulf states, where sugar cane, rice, and tropical fruits are the staple crops. Then comes the temperate zone, with three agricultural subdivisions: (a) the great cotton belt, with Indian corn, sweet potatoes, and the peach, melon, and fig as secondary products. Farther north, in the Central and Middle Atlantic states, we find (b) the region of maize, hemp, and tobacco, with grapes, apples, pears, cherries, and a great variety of garden vegetables as side crops. Finally comes (c) the great wheat-growing region of the North, with buckwheat, hay, and Irish potatoes as subsidiary crops.

Technically, the distribution of the natural zones of vegetation from south to north is classed under the three general heads of Forest, Grass Land, and Arctic Desert, with numerous subdivisions in each.

=330. Boundaries of the zones.=—While the broad continental zones of vegetation follow, in a general way, the climatic zones outlined above, they are not sharply defined, but run into each other and overlap in various degrees, so that a map depicting the range of vegetation in any wide area would show a marked deviation from those of latitude. Various other geographical factors, such as mountain ranges and bodies of water, influence the direction and character of the prevailing winds and rains, and through them the moisture and temperature, to so great an extent that they become the controlling factors over wide areas. In countries bordering on the sea, the coast line always marks a belt of its own, and on the sides of a mountain range, all the climatic zones from the equator to the pole may be repeated during an ascent of a few miles.

In our own country, where the mountain chains and coast lines run approximately north and south, the great continental zones have been superseded, for all practical purposes, by four regional divisions running almost at right angles to them. These are, disregarding minor subdivisions:—

(1) The Forest region, occupying the eastern and south central portion of the Union. In classifying this territory as forest, it is not meant to imply that it is now, or ever was, one unbroken jungle, like parts of central Africa, but that it combines the conditions most favorable to a vigorous and varied forest growth.

(2) The Plains region, extending from the very irregular western boundary of the forest region to the Rocky Mountains.

(3) The Rocky Mountain region, including the Rockies and the Sierra Nevadas with the desert area between them.

(4) The Pacific Slope, a narrow strip between the Sierras and the Pacific Ocean.

The boundaries of these regions, like those of the great continental zones, overlap in various ways, the plants of one region often appearing in another, like an arm of the sea projecting into the land. But the district where any class of plants reaches its highest development is its proper habitat, and as a general thing the one where its cultivation pays best. It would be a waste of time and money to try to raise cotton in Maine, or cranberries in Georgia.

Practical Questions

1. Does the native wild growth of a region furnish any indication of the kind of crops which could be successfully grown there? (325, 326.)

2. Can you give a reason why the zones of cultivation may, in some cases, be more extensive than the natural range of wild plants in the same region? (262, 265.)

3. Can you give reasons why the reverse may sometimes be true? (261, 284.)

4. What crops are raised in different parts of your own state?

5. Name some of the native plants characteristic of different parts of your state. What are its principal plant formations?

Field Work

1. Ecology offers the most attractive subject for field work of all the departments of botany. It can be studied anywhere that a blade of vegetation is to be found. In riding along the railroad, there is an endless fascination in watching the different plant societies succeed one another and noting the variations they undergo with every change of soil or climate.

2. Students in cities can find interesting subjects for study in the vegetation that springs up on vacant lots, around doorsteps and area railings, and even between the paving stones of the more retired streets. On a vacant lot near the public library in Boston, over thirty different kinds of weeds and herbs were found, and in the heart of Washington, D.C., on a vacant space of about twelve by twenty feet, nineteen different species were counted. Just where such things come from, how they get into such positions, and why they stay there, will be interesting questions for city students to solve.

3. But the country always has been and always will be the happy hunting ground of the botanist. All the factors considered in the two preceding sections can hardly be found in any one locality, but by selecting areas traversed by brooks, or by gullies and ravines, very marked changes in the character of vegetation may often be observed. Barren, sandy, or rocky soils, the sunbaked clay of naked hillsides, and the borders of treeless, dusty roads will offer close approximations to xerophyte conditions.

4. If there are any bodies of water in your neighborhood, examine their vegetation and see of what it consists. Notice the difference in the shape and size of floating and immersed leaves and account for it. Note the general absence of free-swimming plants in running water, and account for it. Note the difference between the swamp and border plants and those growing in the water, and what trees or shrubs grow in or near it. Compare the vegetation of different bogs and pools in your neighborhood, and account for any differences you may observe. Compare the water plants with those growing in the dryest and barrenest places in your vicinity, note their differences of structure, and try to find out what special adaptations have taken place in each case. Make a list of those in each location examined that you would class as pioneers.

5. Draw a map of the vegetation of some locality in your neighborhood that presents a variety of conditions, such as a steep hillside, a field or meadow traversed by a brook, the slopes and borders of a ravine, or the change from cultivated ground to uncultivated moor or woodland. Represent the different zones and formations by different colored inks or crayons, or by different degrees of shading with the pencil.

6. Draw a map of your state showing the different agricultural regions, as indicated by the character of the cultivated plants in each; use different colors, or light and dark shading, to define the boundaries. Notice any irregularities of outline and account for them—whether due to soil, moisture, geological formation, winds, or temperature. What is the controlling factor of each region?