Part 3

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

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.

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

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.

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.

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.

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.

ARTIFICIAL KEYS, HOW MADE AND USED

An artificial key is a scheme for easily and quickly identifying any unknown object under consideration. This bulletin being devoted to the trees of Michigan, the keys to be found herein are intended to make it possible for any person, even if his botanical training be meager, to determine what trees grow about any home or farm, city park or woodlot in the state. With certain modifications and limitations they may prove useful in other localities as well. Since many people are unfamiliar with the construction and use of keys for identification, it will be the purpose of the following paragraphs to briefly outline the principles of construction and the manner of using the keys to be found here.

The keys are based on the most striking similarities and differences which the various parts of trees--twigs, buds, leaves, etc.--show, i. e., those characters which stand out in bold relief, which catch the eye at first sight. Two alternatives are presented, either a character is or is not present; these are the only choices possible. Indeed, further divisions are unnecessary and only lead to confusion and possible oversight. The two diametrically opposed characters are said to be coördinate in rank. In the keys they are preceded by the same letter or letters (a and aa or b and bb, etc.) and are set at the same distance from the left margin of the page. Often a and aa, or b and bb are further divisible into other groups; in every case the characters are opposed (a positive and a negative) and are given coördinate rank. It is desirable for mechanical reasons to divide the main divisions of the key more or less evenly, but this is not always feasible, nor should it be religiously adhered to.

Suppose as a concrete example that it is desired to construct a key to distinguish five houses in a city block. Three of these are of wood construction, two are of brick, and of the two wooden houses one is painted white and one brown. We may classify them as follows:

a. Houses wood.

b. Body paint brown. Smith's house bb. Body paint white.

c. Trimmings green color. Jones' house cc. Trimmings slate color. Brown's house

aa. Houses brick.

b. Roof gray slate. Johnson's house bb. Roof red tile. Public Library

It is desirable in many cases to add other characters to lessen the liability of confusion, where the characters chosen are not distinct, and to show the user that he is on the right track. Thus, in the example just given, green color and slate color under certain defects of the eye, a coating of dust or deficiencies of the light might be confused, under which circumstances we would be justified in adding to the above statements without the criticism of description being made. Thus:

bb. c. Trimmings green color; gable roof. Jones' house cc. Trimmings slate color; mansard roof. Brown's house

The keys in this bulletin are constructed on the above principles. They are not in all cases as simple as the illustration just used, but if the reader has mastered the house illustration he will have little or no trouble with the larger keys. Suppose that (during a summer stroll) you come across a large tree with rough, hard bark and thin, lobed leaves which you do not know. Turning to the Summer Key to the Genera you find first a. Leaves simple, and contrasted with this aa. Leaves compound. Obviously the leaf is simple and the genus sought lies in that portion of the key preceding aa, i.e., under a. b and bb under a give you a choice between Leaves needle-shaped, awl-shaped, strap-shaped or scale-like and Leaves broad and flat. The leaf being broad and flat you pass to c and cc under bb. Here you have a choice between Leaves alternate or clustered and Leaves opposite or whorled. Inspection shows the arrangement to be opposite, and you know that the genus sought lies in that portion of the key between cc and aa. Passing to d and dd under cc gives the choice between Margin of leaves entire or only slightly undulate and Margin of leaves serrate to lobed. The leaf is deeply lobed. It is then either a Viburnum or an Acer, and the fact that the leaf-margin is lobed and not finely serrate brings the chase down to Acer. Before going further go back over the key and make careful note of the particular characters which were used to separate this genus from the other genera and try to fix these in mind. This done, turn to the page indicated, where you will find a Summer Key to the Species of Acer. You run through this key in the same manner that you did the genus key. If you have been careful in your search you will finally stop at Acer saccharum. Once more pause and go back over this key and try to fix in mind the characters which were used to separate the various species, especially the difference between your tree and Acer platanoides, which it so closely resembles. This done, turn to the page indicated and compare the characters of your tree with the drawings and descriptions. If you are satisfied with your diagnosis, well and good. If you find that you are wrong, go over the keys again and find wherein you were led astray.

Before you leave the tree take a sample of leaf properly labeled which you can press between the pages of an old magazine and save for future reference. Do this with other trees which you may find and when you get home lay them out side by side so that the labels will not show and compare them. A few trials of this kind will serve to form a mental picture of each leaf which you will remember.