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Table of Contents

Problem.—To discover some of the factors of the environment of plants and animals.

(a) Environment of a plant.

(b) Environment of an animal.

(c) Home environment of a girl or boy.

Laboratory Suggestions

Laboratory demonstrations.—Factors of the environment of a living plant or animal in the vivarium.

Home exercise.—The study of the factors making up my own environment and how I can aid in their control.

Environment.—Each one of us, no matter where he lives, comes in contact with certain surroundings. Air is everywhere around us; light is necessary to us, so much so that we use artificial light at night. The city street, with its dirty and hard paving stones, has come to take the place of the soil of the village or farm. Water and food are a necessary part of our surroundings. Our clothing, useful to maintain a certain temperature, must also be included. All these things—air, light, heat, water, food—together make up our environment.

An unfavorable city environment.

All other animals, and all plants as well, are surrounded by and use practically the same things from their environment as we do. The potted plant in the window, the goldfish in the aquarium, your pet dog at home, all use, as we will later prove, the factors of their environment in the same manner. Air, water, light, a certain amount of heat, soil to live in or on, and food form parts of the surroundings of every living thing.

An experiment that shows the air contains about four fifths nitrogen.

The Same Elements found in Plants and Animals as in their Environment.—It has been found by chemists that the plants and animals as well as their environment may be reduced to about eighty very simple substances known as chemical elements. For example, the air is made up largely of two elements, oxygen and nitrogen. Water, by means of an electric current, may be broken up into two elements, oxygen and hydrogen. The elements in water are combined to make a chemical compound. The oxygen and nitrogen of the air are not so united, but exist as separate gases. If we were to study the chemistry of the bodies of plants and animals and of their foods, we would find them to be made up of certain chemical elements combined in various complex compounds. These elements are principally carbon, hydrogen, oxygen, nitrogen, and perhaps a dozen others in very minute proportions. But the same elements present in the living things might also be found in the environment, for example, water, food, the air, and the soil. It is logical to believe that living things use the chemical elements in their surroundings and in some wonderful manner build up their own bodies from the materials found in their environment. How this is done we will learn in later chapters.

What Plants and Animals take from their Environment. Air.—It is a self-evident fact that animals need air. Even those living in the water use the air dissolved in the water. A fish placed in an air-tight jar will soon die. It will be proven later that plants also need air in order to live.

Apparatus for separating water by means of an electric current into the two elements, hydrogen and oxygen.

Chart to show the percentage of chemical elements in the human body.

Water.—We all know that water must form part of the environment of plants and animals. It is a matter of common knowledge that pets need water to drink; so do other animals. Every one knows we must water a potted plant if we expect it to grow. Water is of so much importance to man that from the time of the Caesars until now he has spent enormous sums of money to bring pure water to his cities. The United States government is spending millions of dollars at the present time to bring by irrigation the water needed to support life in the western desert lands.

Light as Condition of the Environment.—Light is another important factor of the environment. A study of the leaves on any green plant growing near a window will convince one that such plants grow toward the light. All green plants are thus influenced by the sun. Other plants which are not green seem either indifferent or are negatively influenced (move away from) the source of light. Animals may or may not be attracted by light. A moth, for example, will fly toward a flame, an earthworm will move away from light. Some animals prefer a moderate or weak intensity of light and live in shady forests or jungles, prowling about at night. Others seem to need much and strong light. And man himself enjoys only moderate intensity of light and heat. Look at the shady side of a city street on any hot day to prove this statement.

The effect of water upon the growth of trees. These trees were all planted at the same time in soil that is sandy and uniform. They are watered by a small stream which runs from left to right in the picture. Most of the water soaks into the ground before reaching the last trees.

The effect of light upon a growing plant.

Heat.—Animals and plants are both affected by heat or the absence of it. In cold weather green plants either die or their life activities are temporarily suspended—the plant becomes dormant. Likewise small animals, such as insects, may be killed by cold or they may hibernate under stones or boards. Their life activities are stilled until the coming of warm weather. Bears and other large animals go to sleep during the winter and awake thin and active at the approach of warm weather. Animals or plants used to certain temperatures are killed if removed from those temperatures. Even man, the most adaptable of all animals, cannot stand great changes without discomfort and sometimes death. He heats his houses in winter and cools them in summer so as to have the amount of heat most acceptable to him, i.e. about 70° Fahrenheit.

Vegetation in Northern Russia. The trees in this picture are nearly one hundred years old. They live under conditions of extreme cold most of the year.

The Environment determines the Kind of Animals and Plants within It.—In our study of geography we learned that certain luxuriant growths of trees and climbing plants were characteristic of the tropics with its moist, warm climate. No one would expect to find living there the hardy stunted plants of the arctic region. Nor would we expect to find the same kinds of animal life in warm regions as in cold. The surroundings determine the kind of living things there. Plants or animals fitted to live in a given locality will probably be found there if they have had an opportunity to reach that locality. If, for example, temperate forms of life were introduced by man into the tropics, they would either die or they would gradually change so as to become fitted to live in their new environment. Sheep with long wool fitted to live in England, when removed to Cuba, where conditions of greater heat exist, soon died because they were not fitted or adapted to live in their changed environment.

Plant life in a moist tropical forest. Notice the air plants to the left and the resurrection ferns on the tree trunk.

Adaptations.—Plants and animals are not only fitted to live under certain conditions, but each part of the body may be fitted to do certain work. I notice that as I write these words the fingers of my right hand grasp the pen firmly and the hand and arm execute some very complicated movements. This they are able to do because of the free movement given through the arrangement of the delicate bones of the wrist and fingers, their attachment to the bones of the arm, a wonderful complex of muscles which move the bones, and a directing nervous system which plans the work. Because of the peculiar fitness in the structure of the hand for this work we say it is adapted to its function of grasping objects. Each part of a plant or animal is usually fitted for some particular work. The root of a green plant, for example, is fitted to take in water by having tiny absorbing organs growing from it, the stems have pipes or tubes to convey liquids up and down and are strong enough to support the leafy part of the plant. Each part of a plant does work, and is fitted, by means of certain structures, to do that work. It is because of these adaptations that living things are able to do their work within their particular environment.

Plants and Animals and their Natural Environment.—Those of us who have tried to keep potted plants in the schoolroom know how difficult it is to keep them healthy. Dust, foreign gases in the air, lack of moisture, and other causes make the artificial environment in which they are placed unsuitable for them.