Studies of Trees Part 12

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.

[Ill.u.s.tration: FIG. 82.--Black Locust Trees.]

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 cl.u.s.ters 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.

[Ill.u.s.tration: FIG. 83.--Bark of the Honey Locust.]

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.

[Ill.u.s.tration: FIG. 84.--Hardy Catalpa Trees.]

[Ill.u.s.tration: FIG. 85.--Bark of the Flowering Dogwood.]

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 princ.i.p.al 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.

[Ill.u.s.tration: FIG. 86.--The Cross-Section of a Tree.]

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.

[Ill.u.s.tration: FIG. 87.--Characteristic Form and Branching of Trees.

The trees in the photograph are pin oaks.]

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.

[Ill.u.s.tration: FIG. 88.--Roots of a Hemlock Tree in their Search for Water.]

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-tr.i.m.m.i.n.g.

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 cla.s.sification 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.

[Ill.u.s.tration: FIG. 89.--Dead Branches at the Top Caused by Insufficient Water.]

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.