Distinguishing characters: The bud is the largest among the hickories—nearly half an inch long—is hard and oval and covered with yellowish brown downy scales which do not project like those of the shagbark hickory, see Fig. 69. The twigs are extremely coarse. The bark is very tight on the trunk and branches and has a close, hard, wavy appearance as in Fig. 70.
Leaf: The leaf consists of 5, 7 or 9 leaflets all of which are large and pubescent and possess a distinct resinous odor.
Form and size: A tall tree with a broad spreading head.
Range: Eastern North America.
Soil and location: The mockernut hickory grows on a great variety of soils, but prefers one which is rich and well-drained.
Enemies: The same as for the shagbark hickory.
Value for planting: It is not commonly planted.
Commercial value: The wood is similar to that of the shagbark hickory and is put to the same uses.
Other characters: The fruit is a nut, larger and covered with a shell thicker than that of the shagbark. The husk is also thicker and separates into four segments nearly to the base. The kernel is small and sweet.
Other common names: Bigbud hickory; whiteheart hickory.
Comparisons: The pignut hickory (Hicoria glabra), sometimes called broom hickory or brown hickory, often has a shaggy bark, but differs from both the shagbark and the mockernut hickory in possessing buds very much smaller, twigs more slender and leaflets fewer. The nut has a thinner husk which does not separate into four or five segments. The tree prefers drier ground than the other hickories.
The bitternut (Hicoria minima) can be told from the mockernut and other species of hickory by its bud, which has no scales at all. The color of its bud is a characteristic orange yellow. The bark is of a lighter shade than the bark of the mockernut hickory and the leaflets are more numerous than in any of the hickories, varying from 7 to 11. Its nuts are bitter.
Black Walnut (Juglans nigra)
Distinguishing characters: By cutting a twig lengthwise, it will be seen that its pith is divided into little chambers as shown in Fig. 71. The bud is dark gray and satiny. The bark is dark brown and deeply ridged and the fruit is the familiar round walnut.
Form and size: A tall tree with a spreading crown composed of stout branches. In the open it grows very symmetrically.
Range: Eastern United States.
Soil and location: The black walnut prefers a deep, rich, fertile soil and requires a great deal of light.
Enemies: The tree is a favorite of many caterpillars.
Value for planting: It forms a beautiful spreading tree on open ground, but is not planted to any extent because it is hard to transplant. It grows slowly unless the soil is very deep and rich, develops its leaves late in the spring and sheds them early in the fall and produces its fruit in great profusion.
Commercial value: The wood is heavy, strong, of chocolate brown color and capable of taking a fine polish. It is used for cabinet making and interior finish of houses. The older the tree, usually, the better the wood, and the consumption of the species in the past has been so heavy that it is becoming rare. The European varieties which are frequently planted in America as substitutes for the native species yield better nuts, but the American species produces better wood.
Other characters: The fruit is a large round nut about two inches in diameter, covered with a smooth husk which at first is dull green in color and later turns brown. The husk does not separate into sections. The kernel is edible and produces an oil of commercial value.
The leaves are compound and alternate with 15 to 23 leaflets to each.
Comparisons: The butternut (Juglans cinerea) is another tree that has the pith divided into little chambers, but the little chambers here are shorter than in the black walnut, as may be seen from a comparison of Figs. 71 and 72. The bark of the butternut is light gray while that of the black walnut is dark. The buds in the butternut are longer than those of the black walnut and are light brown instead of gray in color. The form of the tree is low and spreading as compared with the black walnut. The fruit in the butternut is elongated while that of the black walnut is round. The leaves of the butternut have fewer leaflets and these are lighter in color.
Group X. Tulip Tree, Sweet Gum, Linden, Magnolia, Locust, Catalpa, Dogwood, Mulberry and Osage Orange
Tulip Tree (Liriodendron tulipifera)
Distinguishing characters: There are four characters that stand out conspicuously in the tulip tree—the bud, the trunk, the persistent fruit cups and the wedged leaf.
The bud, Fig. 74, about three-quarters of an inch long, is covered by two purplish scales which lend special significance to its whole appearance. The trunk is extremely individual because it rises stout and shaft-like, away above the ground without a branch as shown in Fig. 73. The tree flowers in the latter part of May but the cup that holds the fruit persists throughout the winter. The leaf, Fig. 75, has four lobes, is nearly as broad as it is long and so notched at the upper end that it looks different from any other leaf.
Form and size: The tulip tree is one of the largest, stateliest and tallest of our trees.
Range: Eastern United States.
Soil and location: Requires a deep, moist soil.
Enemies: Comparatively free from insects and disease.
Value for planting: The tree has great value as a specimen on the lawn but is undesirable as a street tree because it requires considerable moisture and transplants with difficulty. It should be planted while young and where it can obtain plenty of light. It grows rapidly.
Commercial value: The wood is commercially known as whitewood and yellow poplar. It is light, soft, not strong and easily worked. It is used in construction, for interior finish of houses, woodenware and shingles. It has a medicinal value.
Other characters: The flower, shown in Fig. 75, is greenish yellow in color, appears in May and resembles a tulip; hence the name tulip tree. The fruit is a cone.
Other common names: Whitewood; yellow poplar; poplar and tulip poplar.
Sweet Gum (Liquidambar styraciflua)
Distinguishing characters: The persistent, spiny, long-stemmed round fruit; the corky growths on the twigs, the characteristic star-shaped leaves (Fig. 76) and the very shiny greenish brown buds and the perfect symmetry of the tree are the chief characters by which to identify the species.
Form and size: The sweet gum has a beautiful symmetrical shape, forming a true monopodium.
Range: From Connecticut to Florida and west to Missouri.
Soil and location: Grows in any good soil but prefers low wet ground. It grows rapidly and needs plenty of light.
Enemies: Is very often a favorite of leaf-eating caterpillars.
Value for planting: The tree is sought for the brilliant color of its foliage in the fall, and is suitable for planting both on the lawn and street. In growing the tree for ornamental purposes it is important that it should be frequently transplanted in the nursery and that it be transported with burlap wrapping around its roots.
Commercial value: The wood is reddish brown in color, tends to splinter and is inclined to warp in drying. It is used in cooperage, veneer work and for interior finish.
Other characters: On the smaller branches there are irregular developments of cork as shown in Fig. 76, projecting in some cases to half an inch in thickness.
Other common names: Red gum.
Comparisons: The cork elm is another tree that possesses corky ridges along its twigs, but this differs from the sweet gum in wanting the spiny fruit and its other distinctive traits.
American Linden (Tilia Americana)
Distinguishing characters: The great distinguishing feature of any linden is the one-sided character of its bud and leaf. The bud, dark red and conical, carries a sort of protuberance which makes it extremely one sided as shown in Fig. 77. The leaf, Fig. 78, is heart-shaped with the side nearest the branch largest.
Form and size: The American Linden is a medium-sized tree with a broad round head.
Range: Eastern North America and more common in the north than in the south.
Soil and location: Requires a rich, moist soil.
Enemies: Its leaves are a favorite food of caterpillars and its wood is frequently attacked by a boring insect known as the linden borer (Saperda vestita).
Value for planting: The linden is easily transplanted and grows rapidly. It is used for lawn and street planting but is less desirable for these purposes than the European species.
Commercial value: The wood is light and soft and used for paper pulp, woodenware, cooperage and furniture. The tree is a favorite with bee keepers on account of the large quantities of nectar contained in its flowers.
Other characters: The fruit is like a pea, gray and woody. The flowers appear in early July, are greenish-yellow and very fragrant.
Other common names: Bass-wood; lime-tree; whitewood.
Comparisons: The European lindens, Fig. 79, of which there are several species under cultivation, differ from the native species in having buds and leaves smaller in size, more numerous and darker in color.
The Magnolias
The various species of magnolia trees are readily distinguished by their buds. They all prefer moist, rich soil and have their principal value as decorative trees on the lawn. They are distinctly southern trees; some species under cultivation in the United States come from Asia, but the two most commonly grown in the Eastern States are the cucumber tree and the umbrella tree.
Cucumber Tree (Magnolia acuminata)
Distinguishing characters: The buds are small and slender compared with those of the other magnolia trees and are covered with small silvery silky hairs. The habit of the tree is to form a straight axis of great height with a symmetrical mass of branches, producing a perfect monopodial crown. The tree is sometimes known as mountain magnolia.
Umbrella Tree (Magnolia tripetala)
Distinguishing characters: The buds, Fig. 80, are extremely long, often one and a half inches, have a purple color and are smooth. The tree does not grow to large size and produces an open spreading head. Its leaves, twelve to eighteen inches long, are larger than those of the other magnolia trees. The tree is sometimes called elkwood.
Black Locust (Robinia pseudacacia)
Distinguishing characters: The bark of the trunk is rough and deeply ridged, as shown in Fig. 81. The buds are hardly noticeable; the twigs sometimes bear small spines on one side. The leaves are large, compound, and fern-like. The individual leaflets are small and delicate.
Form and size: The locust is a medium-sized tree developing a slender straight trunk when grown alongside of others; see Fig. 82.
Range: Canada and United States.
Soil and location: The locust will grow on almost any soil except a wet, heavy one. It requires plenty of light.
Enemies: The locust borer has done serious damage to this tree. The grubs of this insect burrow in the sapwood and kill the tree or make it unfit for commercial use. The locust miner is a beetle which is now annually defoliating trees of this species in large numbers.
Value for planting: It has little value for ornamental planting.
Commercial value: Though short-lived, the locust grows very rapidly. It is extremely durable in contact with the soil and possesses great strength. It is therefore extensively grown for fence-posts and railroad ties. Locust posts will last from fifteen to twenty years. The wood is valuable for fuel.
Other characters: The flowers are showy pea-shaped panicles appearing in May and June. The fruit is a small pod.
Other common names: Yellow locust; common locust; locust.
Comparisons: The honey locust (Gleditsia triacanthos) can be told from the black locust by the differences in their bark. In the honey locust the bark is not ridged, has a sort of dark iron-gray color and is often covered with clusters of stout, sharp-pointed thorns as in Fig. 83. The fruit is a large pod often remaining on the tree through the winter. This tree has an ornamental, but no commercial value.
Hardy Catalpa (Catalpa speciosa)
Distinguishing characters: The tree may be told by its fruit, which hang in long slender pods all winter. The leaf-scars appear on the stem in whorls of three and rarely opposite each other.
Form and size: The catalpa has a short, thick and twisted trunk with an irregular head.
Range: Central and eastern United States.
Soil and location: It grows naturally on low bottom-lands but will also do well in poor, dry soils.
Enemies: Practically free from disease and insects.
Value for planting: The catalpa grows very rapidly and is cultivated in parks for ornament and in groves for commercial purposes. The hardy catalpa is preferable to the common catalpa for planting.
Commercial value: The wood is extremely durable in contact with the soil and is consequently used for posts and railroad ties.
Other characters: The flowers, which appear in late June and early July, are large, white and very showy.
Other common names: Indian bean; western catalpa.
Comparisons: The white flowering dogwood (Cornus florida) is a small tree which also has its leaves in whorls of three or sometimes opposite. It can be readily told from other trees, however, by the small square plates into which the outer bark on the trunk divides itself, see Fig. 85, and by the characteristic drooping character of its branches. It is one of the most common plants in our eastern deciduous forests. It is extremely beautiful both in the spring and in the fall and is frequently planted for ornament. There are many varieties of dogwood in common use.
White Mulberry (Morus alba)
A small tree recognized by its small round reddish brown buds and light brown, finely furrowed (wavy looking) bark.
The tree, probably a native of China, is grown under cultivation in eastern Canada and United States. It grows rapidly in moist soil and is not fastidious in its light requirements. Its chief value is for screening and for underplanting in woodlands.
The red mulberry (Morus rubra) is apt to be confused with the white mulberry, but differs in the following characters: The leaves of the red mulberry are rough on the upper side and downy on the under side, whereas the leaves of the white mulberry are smooth and shiny. The buds in the red are larger and more shiny than those of the white.
The Osage orange (Toxylon pomiferum) is similar to the mulberry in the light, golden color of its bark, but differs from it in possessing conspicuous spines along the twigs and branches and a more ridged bark.
Chapter IV
The Structure and Requirements of Trees
To be able fully to appreciate trees, their mode of life, their enemies and their care, one must know something of their structure and life requirements.
Structure of trees: Among the lower forms of plants there is very little distinction between the various parts—no differentiation into root, stem, or crown. Often the lower forms of animal and vegetable life are so similar that one cannot discriminate between them. But as we ascend in the scale, the various plant forms become more and more complex until we reach the tree, which is the largest and highest form of all plants. The tree is a living organism composed of cells like any other living organism. It has many parts, every one of which has a definite purpose. The three principal parts are: the stem, the crown, and the root.
The stem: If we examine the cross-section of a tree, Fig. 86, we will notice that it is made up of numerous rings arranged in sections of different color and structure. The central part is known as the pith. Around the pith comes a dark, close-grained series of rings known as the heartwood, and outside the heartwood comes a lighter layer, the sapwood. The cambium layer surrounds the sapwood and the bark covers all. The cambium layer is the most important tissue of the tree and, together with part of the sapwood, transports the water and food of the tree. It is for this reason that a tree may be hollow, without heart and sapwood, and still produce foliage and fruit.
The crown: The crown varies in form in different species and is developed by the growth of new shoots from buds. The bud grows out to a certain length and forms the branch. Afterwards it thickens only and does not increase in length. New branches will then form from other buds on the same branch. This explains in part the characteristic branching of trees, Fig. 87.
The leaves are the stomach and lungs of the tree. Their broad blades are a device to catch the sunlight which is needed in the process of digesting the food of the tree. The leaves are arranged on the twigs in such a way as to catch the most sunlight. The leaves take up the carbonic acid gas from the air, decompose it under the influence of light and combine it with the minerals and water brought up by the roots from the soil. The resulting chemical combinations are the sugars and starches used, by the cambium layer in building up the body of the tree. A green pigment, chlorophyll, in the leaf is the medium by which, with the aid of sunlight, the sugars are manufactured.
The chlorophyll gives the leaf its green color, and this explains why a tree pales when it is in a dying condition or when its life processes are interfered with. The other colors of the leaf—the reds, browns and yellows of the fall or spring—are due to other pigments. These are angular crystals of different hues, which at certain times of the year become more conspicuous than at others, a phenomenon which explains the variation in the colors of the leaves during the different seasons.
It is evident that a tree is greatly dependent upon its leaves for the manufacture of food and one can, therefore, readily see why it is important to prevent destruction of the leaves by insects or through over-trimming.
The root: The root develops in much the same manner as the crown. Its depth and spread will vary with the species but will also depend somewhat upon the condition of the soil around it. A deep or a dry soil will tend to develop a deep root, while a shallow or moist soil will produce a shallow root, Fig. 88.
The numerous fine hairs which cover the roots serve the purpose of taking up food and water from the soil, while the heavy roots help to support the tree. The root-hairs are extremely tender, are easily dried out when exposed to the sun and wind, and are apt to become overheated when permitted to remain tightly packed for any length of time. These considerations are of practical importance in the planting of trees and in the application of fertilizers. It is these fine rootlets far away from the trunk of the tree that have to be fed, and all fertilizers must, therefore, be applied at points some distance from the trunk and not close to it, where merely the large, supporting roots are located. In the cultivation of trees the same principle holds true.
Requirements of trees: Trees are dependent upon certain soil and atmospheric conditions which influence their growth and development.
(1) Influence of moisture: The form of the tree and its growth and structure depend greatly upon the supply of moisture. Botanists have taken the moisture factor as the basis of classification and have subdivided trees into those that grow in moist places (hydrophytes), those that grow in medium soils (mesophytes), and those that grow in dry places (xerophytes). Water is taken up by the roots of the tree from the soil. The liquid absorbed by the roots carries in solution the mineral salts—the food of the tree—and no food can be taken up unless it is in solution. Much of the water is used by the tree and an enormous amount is given off in the process of evaporation.
These facts will explain some of the fundamental principles in the care of trees. To a tree growing on a city street or on a lawn where nature fails to supply the requisite amount of water, the latter must be supplied artificially, especially during the hot summer months, or else dead branches may result as seen in Fig. 89. Too much thinning out of the crown causes excessive evaporation, and too much cutting out in woodlands causes the soil to dry and the trees to suffer for the want of moisture. This also explains why it is essential, in wooded areas, to retain on the ground the fallen leaves. In decomposing and mixing with the soil, the fallen leaves not only supply the trees with food material, but also tend to conserve moisture in the ground and to prevent the drying out of the soil. Raking off the leaves from wooded areas, a practice common in parks and on private estates—hurts the trees seriously. Some soils may have plenty of moisture, but may also be so heavily saturated with acids or salts that the tree cannot utilize the moisture, and it suffers from drought just the same as if there had been no moisture at all in the soil. Such soils are said to be “physiologically dry” and need treatment.
In the development of disease, moisture is a contributing factor and, therefore, in cavities or underneath bandages where there is likely to be an accumulation of moisture, decay will do more damage than in places that are dry and exposed to the sun.
(2) Influence of soil: Soil is made up of fine particles of sand and rock and of vegetable matter called humus. A tree will require a certain soil, and unsuitable soils can be very often modified to suit the needs of the tree. A deep, moderately loose, sandy loam, however, which is sufficiently aerated and well supplied with water, will support almost any tree. Too much of any one constituent will make a soil unfit for the production of trees. If too much clay is present the soil becomes “stiff.” If too much vegetable matter is present, the soil becomes “sour.” The physical character of the soil is also important. By physical character is meant the porosity which results from breaking up the soil. This is accomplished by ploughing or cultivation. In nature, worms help to do this for the soil, but on streets an occasional digging up of the soil about the base of the tree is essential.
Humus or the organic matter in the soil is composed of litter, leaves and animal ingredients that have decayed under the influence of bacteria. The more vegetable matter in the humus, the darker the soil; and therefore a good soil such as one finds on the upper surface of a well-tilled farm has quite a dark color. When, however, a soil contains an unusual quantity of humus, it is known as “muck,” and when there is still more humus present we find peat. Neither of these two soils is suitable for proper tree growth.
(3) Influence of light: Light is required by the leaves in the process of assimilation. Cutting off some of the light from a tree affects its form. This is why trees grown in the open have wide-spreading crowns with branches starting near the ground as in Fig. 90, while the same species growing in the forest produces tall, lanky trees, free from branches to but a few feet from the top as in Fig. 91. Some trees can endure more shade than others, but all will grow in full light. This explains why trees like the beech, hemlock, sugar maple, spruce, holly and dogwood can grow in the shade, while the poplar, birch and willow require light. It also explains why, in the forest, the lower branches die and fall off—a process known in Forestry as “natural pruning,” The influence of light on the form of trees should be well understood by all those who plant trees and by those designing landscape effects.
(4) Influence of heat: Trees require a certain amount of heat. They receive it partly from the sun and partly from the soil. Evaporation prevents the overheating of the crown. The main stem of the tree is heated by water from the soil; therefore trees in the open begin growth in the spring earlier than trees in the forest because the soil in the open is warmer. Shrubs begin their growth earlier than trees because of the nearness of their crowns to their root systems. This also explains why a warm rain will start vegetation quickly. Too much heat will naturally cause excessive drying of the roots or excessive evaporation from the leaves and therefore more water is needed by the tree in summer than in winter.
(5) Influence of season and frost: The life processes of a tree are checked when the temperature sinks below a certain point. The tree is thus, during the winter, in a period of rest and only a few chemical changes take place which lead up to the starting of vegetation. In eastern United States, growth starts in April and ceases during the latter part of August or in early September. The different parts of a tree may freeze solid during the winter without injury, provided the tree is a native one. Exotic trees may suffer greatly from extreme cold. This is one of the main reasons why it is always advisable to plant native trees rather than those that are imported and have not yet been acclimatized. Frosts during mid-winter are not quite as injurious as early and late frosts and, therefore, if one is going to protect plants from the winter’s cold, it is well to apply the covering early enough and to keep it on late enough to overcome this difficulty.
The mechanical injuries from frost are also important. Snow and sleet will weigh down branches but rarely break them, while frost will cause them to become brittle and to break easily. Those who climb and prune trees should be especially cautious on frosty days.
(6) Influence of air: On the under side of leaves and on other surfaces of a tree little pores known as stomata may be found. In the bark of birch and cherry trees these openings are very conspicuous and are there known as lenticels. These pores are necessary for the breathing of the tree (respiration), whereby carbonic acid gas is taken in from the air and oxygen given out. The process of assimilation depends upon this breathing process and it is therefore evident that when the stomata are clogged as may occur where a tree is subjected to smoke or dust, the life processes of the tree will be interfered with. The same injurious effect results when the stomata of the roots are interfered with. Such interference may occur in cases where a heavy layer of soil is piled around the base of a tree, where the soil about the base of a tree is allowed to become compact, where a tree is planted too deep, or where the roots are submerged under water for any length of time. In any case the air cannot get to the roots and the tree suffers. Nature takes special cognizance of this important requirement in the case of cypress trees, which habitually grow under water. Here the trees are provided with special woody protuberances known as “cypress knees,” which emerge above water and take the necessary air. See Fig. 18.
Conclusions: From the foregoing it will be seen that trees have certain needs that nature or man must supply. These requirements differ with the different species, and in all work of planting and care as well as in the natural distribution of trees it is both interesting and necessary to observe these individual wants, to select species in accordance with local conditions and to care for trees in conformity with their natural needs.