Читать книгу Michigan Trees: A Handbook of the Native and Most Important Introduced Species - Charles Herbert Otis - Страница 6

Table of Contents

People are everywhere associated with trees. Trees give cooling shade in our parks and dooryards and along our highways; they lend their beauty to the landscape and relieve it of monotony; they yield many kinds of fruits, some of which furnish man and the animals of the forest with food; and they furnish vast quantities of lumber for a multitude of uses. How important it is, then, that every person, whether school-child or grown-up, should become acquainted with our trees. Most people know a few of our commonest trees, but are ignorant of the great wealth of tree forms about them. Some who may have wished to go further have been hindered for lack of a teacher or dismayed by the very multitude of manuals to which they have had access.

In beginning a study of the trees the student should start on a solid foundation, eliminating the uncertainties and the errors which no doubt have appeared and retaining only the established facts. Once started he should go slowly, assimilating each new discovery before seeking another. He should begin with the trees nearest home, and, as he gradually grows to know these in all their aspects, should extend his trips afield. Not only should he be able to name the trees when they are fully clothed in their summer dress, but he should as readily know these same trees when the leaves have fallen and only the bare branches stand silhouetted against the sky. Then, and only then, will he derive the utmost satisfaction from his efforts.

The characters which are used in studying the trees are habit, leaves, flowers, fruit, buds, bark, distribution and habitat. These will be discussed briefly in the next few pages, the same order that is used in the detailed descriptions of species being maintained in the present discussion. A few drawings will also be added to make clear certain points and to show comparative forms.

NAME.—Every tree has one or several common names and a scientific or Latin name. Some of these common names are merely local, others have a more extended use. Some few names apply to totally different species. Thus, Cottonwood in Michigan is Populus deltoides, in Idaho and Colorado Populus angustifolia, in California Populus fremontii and in Kentucky Tilia heterophylla. While it should not be forgotten that in common speech it is proper as well as convenient to call trees by their common names, yet, in view of the many uncertainties pertaining to their use, a scientific name is at times absolutely essential to the clear understanding of what is meant. Latin is the language in universal use by all scientists. No longer used by any civilized nation, it has become a dead language and consequently never changes. Its vocabulary and its constructions will a thousand years hence be the same as they are today. Being in universal use among scientists of all nationalities no confusion arises from the use of a Latin word. The Oak in Germany is known as Eiche, in France as chêne and in Spain as roble, but the Latin word Quercus is the same for all these countries.

A scientific name as applied to trees consists of at least two parts, as Quercus alba; the first named is the genus and is always written with a capital letter, the second is the species and is written with a small letter, the two names constituting the briefest possible description of the particular tree. It is customary to add to these the name or an abbreviation of the name of the person who first gave the name to the tree, as Quercus alba L., the abbreviation standing for Linnaeus. Sometimes a third name is used, as Acer saccharum nigrum, referring in this case to a variety of the ordinary Sugar Maple.

Genera which bear a relationship to each other are placed in the same family, the family name always having the characteristic ending—aceae. Related families are again grouped into orders, with the characteristic ending—ales. Orders are in like manner arranged into larger groups, called classes, and the latter into still larger groups, divisions, etc., each with its characteristic ending. Thus, Acer saccharum nigrum (Michx. f.) Britt. is classified as follows:

Division—Spermatophyta

Subdivision—Angiospermae

Class—Dicotyledoneae

Order—Sapindales

Family—Aceraceae

Genus—Acer

Species—saccharum

Variety—nigrum.

HABIT.—Habit, or the general appearance of a plant, is an important character of identification, especially as we become more and more familiar with the trees. Two main types are recognized, based on the manner of branching of the trunk, the upright and the spreading. In the one the trunk extends straight upwards without dividing, as is typical in most of the conifers, and in the other the trunk divides to form several large branches and the broad, spreading crown of most of our broad-leaf trees. The crown in either case may be regular in outline or very irregular, straggling or straight-limbed. Moreover, the tree growing in the open, where there is no crowding and there is plenty of light, may differ very greatly from the tree in the forest, where the struggle for existence becomes very keen. A short, thick trunk and low, spreading, many-branched crown characterizes the tree in the open, whereas the forest tree has a long, slender, clean trunk and a narrow crown of few branches. In the descriptions of trees in this bulletin, unless otherwise stated, the habit in the open is the one given. Again, the tree may have been injured by storm or insect at some period of its growth and its natural symmetry destroyed. Moreover, the age of a tree has a great influence on its outline, young trees being generally narrow and more or less conical, broadening out as they become older. We may say, then, that each tree has an individuality of its own, little eccentricities similar to those that make people different from one another. And just as we have little difficulty in recognizing our friends at a distance by some peculiarity of walk or action, so are we able to recognize a great many trees at a distance by some peculiarity of form or habit.

I. LEAF OUTLINES

Lanceolate.	Ovate.	Heart-shaped.	Halberd-shaped.	Linear.	Elliptical.

Oblong.	Oval.	Orbicular.	Oblanceolate.	Spatulate.	Obovate.

II. LEAF TIPS

Acuminate.	Acute.	Obtuse.	Emarginate.	Mucronate.

LEAVES.—With the advent of spring the buds of our broad-leaf trees swell and burst and the leaves come forth and clothe the trees with mantles of green, hiding the branches which have been bare through the cold winter months. The evergreens, too, take on new color and begin a new period of growth. It is the leaves which the beginner finds most interesting and in which he finds a ready means of identification. It must be remembered, however, that leaves vary greatly in size and shape and general appearance. How large are the leaves on a flourishing sprout and how small on a stunted tree of the same species growing near by, but under adverse circumstances. How different are the leaves of the big white oak standing in the yard; they are hardly lobed on the lowermost branches, while higher up they are deeply cut. Yet, in spite of the many modifications that leaves undergo, the leaves of any one species have certain rather constant characters which are found in all forms, and the student will have little difficulty in selecting and recognizing typical leaves.

III. LEAF MARGINS

Serrate. Doubly Serrate. Crenate. Undulate. Sinuate. Lobed. Dentate.

Leaves are either persistent, as in most of our conifers, which stay green all winter, or they turn various colors with the frost and fall early in autumn; often they hang dead and lifeless far into the winter. The points about leaves which we are accustomed to consider are the position or arrangement of the leaves on the branch, whether simple or compound, size, shape, texture, color, amount and character of pubescence, character of the margin, venation, etc. The following diagrams will serve to illustrate some of the ordinary forms and shapes of leaves, their margins, etc.

IV. PARTS OF A FLOWER

Perfect Flower. Stamen. Pistil.

a. Sepal (Calyx).	f. Filament.
b. Petal (Corolla).	g. Stigma.
c. Stamen.	h. Style.
d. Pistil.	i. Ovary.
e. Anther.

FLOWERS.—Every tree when old enough bears flowers in its proper season. Some of these, as the Catalpas, Locusts and Horse-chestnuts are very showy, others, like the Oaks and Hickories, are comparatively inconspicuous; some are brilliantly colored, others are of the same color as the leaves. Nevertheless, the flowers are very accurate means of classification, and their only drawback is that they last for such a short period of time each year.

Just as we have male and female in the animal world, so we have male and female in the plant world. A few of our trees, as the Locust, Basswood and Cherries have perfect flowers, bearing both stamens and pistil. The great majority, however, have unisexual flowers, bearing stamens or pistils, but not both. When both male and female flowers are found on the same tree, the flowers are said to be monoecious, and when male flowers occur on one tree and the female on a different tree, the flowers are said to be dioecious. The Cottonwood is dioecious, and the little seeds are surrounded by a tuft of long, white hairs which enables the wind to carry them to considerable distances from the parent tree, to the disgust of people living within range. Many cities forbid the planting of Cottonwood on account of the “cotton.” Since in some cases it is desirable to plant this rapid-growing tree, as in cities burning large amounts of soft coal, it is a distinct advantage to know that male trees are lacking in the objectionable “cotton” and may be planted safely.

V. TYPES OF INFLORESCENSES

Spike.	Raceme.	Panicle.	Corymb.	Umbel.	Cyme.

Before trees can produce fruit their flowers must be fertilized, i.e., pollen from the anther of a stamen must come in contact with the stigma of a pistil. Some flowers are self-fertilized, others are cross-fertilized. For a long time it was not known how fertilization was accomplished, but now we know that many insects, like the nectar-loving bees and butterflies, and in other cases the wind transport the pollen from one flower to another, often miles being traversed before the right kind of flower or a flower in the right stage of development is found. And many are the modifications of flowers to insure this transference of pollen.

FRUIT.—So numerous and so varied are the forms of tree fruits that it would only be confusing to enumerate their various characters. Some fruits, as the achenes of the Poplars and Willows, are so small and light that they are carried long distances by the wind; others, like the hickory nuts and walnuts, are too heavy to be wind-blown. Many fruits are of considerable economic and commercial importance and are gathered and marketed on a large scale; such are the hickory nuts, walnuts, chestnuts, etc. Some, not esteemed by man, form an important article of diet for the birds and small animals of the forest. Unfortunately, there are a number of limitations to the usefulness of fruit for identification purposes. Some trees require years to mature their fruit. Many trees, while producing an abundance of fruit at certain intervals, bear none at all or only very small and uncertain quantities between the years of abundance. Again, in the case of dioecious trees, only the female or pistillate bear fruit. Notwithstanding these limitations tree fruits are a very valuable aid to the student, and he should always search closely for evidences of their presence and character.

VI. WINTER

TWIG OF RED

MULBERRY

a. Tip-scar.

b. Lateral bud.

c. Leaf-scar.

d. Stipule-scars.

WINTER-BUDS.—Buds, with their accompanying leaf-and stipule-scars form the basis of tree identification in winter. The size, color, position with reference to the twig, number and arrangement and character of bud-scales, etc., are all characters of the greatest value in winter determinations. Buds are either terminal or lateral, depending on their position on the twig. A lateral bud is one situated on the side of a twig in the axil of a leaf-scar. A terminal bud is one situated at the end of a twig, where it is ready to continue the growth of the twig the following spring. In the keys an important consideration is the presence or absence of the terminal bud. Inasmuch as the determination of this point gives the beginner some trouble at first, it is hoped that the accompanying diagrams and explanatory remarks will make the distinction clear.

VII. WINTER

TWIG OF BLACK

WALNUT

a. Terminal bud.

b. Lateral bud.

c. Leaf-scar.

d. Bundle-scars.

e. Pith.

In the Elms, Willows, Basswood and many other species the terminal bud and a small portion of the tip of the twig dies and drops off in late autumn, leaving a small scar at the end of the twig (a, fig. VI). The presence of this tip-scar indicates that the terminal bud is absent. Often a lateral bud will be found very close to the tip-scar (b, fig. VI), which, bending into line with the twig, makes it appear terminal. However, the presence of a leaf-scar immediately below it shows it to be a lateral bud (c, fig. VI). In some large twigs the eye unaided will serve to find the tip-scar, but with the smaller twigs a hand-lens is necessary.

The arrangement, size and shape of the leaf-scars (c, fig. VII) are important factors in identification by winter characters. Within the leaf-scars are one or more dots (d, fig. VII), sometimes quite inconspicuous, often very prominent. These are the scars left by the fibro-vascular bundles which run through the petiole into the blade of the leaf, and are designated as bundle-scars. There may be only one as in Sassafras and Hackberry, two as in Ginkgo, three as in the Poplars and Cherries, or many; and they may be arranged in a U- or V-shaped line, or they may be without definite order. Often stipule-scars (d, fig. VI) occur on either side of the leaf-scar; these are scars left by the fall of a pair of small leaflets called stipules and located at the base of the leaves, and their form varies according to the form of the stipules which made them.

BARK.—The woodsman uses the bark of a tree more than any other character in distinguishing the trees about him, and he is often able to use this character alone with much accuracy at great distances. However, the appearance of bark differs so greatly with the age of the tree and with its environment that it is difficult to describe it accurately. Some characters are distinctive, however, and serve as a ready means of identification; such characters are the peeling of the Sycamore and Paper Birch, the “shagging” of the Shagbark Hickory, the spicy taste of Sassafras bark and the mucilaginous inner bark of the Slippery Elm.

WOOD.—It is not expected that the information given under this heading will be of any particular value in identifying living trees. Often, however, the student finds himself in the midst of felling operations, when the information concerning the wood is of considerable value.

DISTRIBUTION AND HABITAT.—To a lesser extent do distribution and habitat of a species aid in the identification of a tree. It is a distinct aid to know that the Chestnut is native in south-eastern Michigan only and that the Mountain Ash does not extend south of Ludington. So too, knowing the water-loving habit of the Swamp White Oak, we would not expect to find this same tree flourishing on the top of a hard, dry hill.

The characters, then, which are used to identify the trees about us are many. Not all will be available at any one time, not all have been mentioned in the foregoing pages nor in the manual. It is our opinion, however, that the student will not be greatly handicapped by this lack of detail, but rather that he will take great interest and genuine pleasure in discovering these things for himself.