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.
[Illustration: 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.
A goldfish placed in a small glass jar with no food or no green water plants soon seeks the surface of the water, and if the water is not changed frequently so as to supply air the fish will die. Again the artificial environment lacks something that the fish needs. Each plant and animal is limited to a certain environment because of certain individual needs which make the surroundings fit for it to live in.
[Illustration: A natural barrier on a stream. No trout would be found above this fall. Why not?]
Changes in Environment.--Most plants and animals do not change their environment. Trees, green plants of all kinds, and some animals remain fixed in one spot practically all their lives. Certain tiny plants and most animals move from place to place, either in air, water, on the earth or in the earth, but they maintain relatively the same conditions in environment.
Birds are perhaps the most striking exception, for some may fly thousands of miles from their summer homes to winter in the south. Other animals, too, migrate from place to place, but not usually where there are great changes in the surroundings. A high mountain chain with intense cold at the upper altitudes would be a barrier over which, for example, a bear, a deer, or a snail could not travel. Fish like trout will migrate up a stream until they come to a fall too high for them to jump. There they must stop because their environment limits them.
[Illustration: A new apartment house, with out-of-door sleeping porch.]
Man in his Environment.--Man, while he is like other animals in requiring heat, light, water, and food, differs from them in that he has come to live in a more or less artificial environment. Men who lived on the earth thousands of year ago did not wear clothes or have elaborate homes of wood or brick or stone. They did not use fire, nor did they eat cooked foods. In short, by slow degrees, civilized man has come to live in a changed environment from that of other animals. The living together of men in communities has caused certain needs to develop. Many things can be supplied in common, as water, milk, foods. Wastes of all kinds have to be disposed of in a town or city. Houses have come to be placed close together, or piled on top of each other, as in the modern apartment. Fields and trees, all outdoor life, has practically disappeared. Man has come to live in an artificial environment.
Care and Improvement of One's Environment.--Man can modify or change his surroundings by making this artificial environment favorable to live in. He may heat his dwellings in winter and cool them in summer so as to maintain a moderate and nearly constant temperature. He may see that his dwellings have windows so as to let light and air pass in and out. He may have light at night and shade by day from intense light. He may have a system of pure water supply and may see that drains or sewers carry away his wastes. He may see to it that people ill with "catching" or _infectious_ diseases are isolated or _quarantined_ from others. This care of the artificial environment is known as _sanitation_, while the care of the _individual_ for himself within the environment is known as _hygiene_. It will be the chief end of this book to show girls and boys how they may become good citizens through the proper control of personal hygiene and sanitation.
REFERENCE BOOKS
ELEMENTARY
Hunter, _Laboratory Problems in Civic Biology_. American Book Company.
Hough and Sedgwick, _Elements of Hygiene and Sanitation_.
Ginn and Company.
Jordan and Kellogg, _Animal Life_. Appleton.
Sharpe, _A Laboratory Manual for the Solution of Problems in Biology_, _p. 95_. American Book Company.
Tolman, _Hygiene for the Worker_. American Book Company.
ADVANCED
Allen, _Civics and Health_. Ginn and Company.
III. THE INTERRELATIONS OF PLANTS AND ANIMALS
_Problem.--To discover the general interrelations of green plants and animals._ _(a) Plants as homes for insects._ _(b) Plants as food for insects._ _(c) Insects as pollinating agents._
LABORATORY SUGGESTIONS
_A field trip_:--Object: to collect common insects and study their general characteristics; to study the food and shelter relation of plant and insects. The pollination of flowers should also be carefully studied so as to give the pupil a general viewpoint as an introduction to the study of biology.
_Laboratory exercise._--Examination of simple insect, identification of parts--drawing. Examination and identification of some orders of insects.
_Laboratory demonstration._--Life history of monarch and some other butterflies or moths.
_Laboratory exercise._--Study of simple flower--emphasis on work of essential organs, drawing.
_Laboratory exercise._--Study of mutual adaptations in a given insect and a given flower, _e.g._ butter and eggs and bumble bee.
_Demonstration of examples of insect pollination._
The Object of a Field Trip.--Many of us live in the city, where the crowded streets, the closely packed apartments, and the city playgrounds form our environment. It is very artificial at best. To understand better the _normal environment_ of plants or animals we should go into the country.
Failing in this, an overgrown city lot or a park will give us much more closely the environment as it touches some animals lower than man. We must then remember that in learning something of the natural environment of other living creatures we may better understand our own environment and our relation to it.
On any bright warm day in the fall we will find insects swarming everywhere in any vacant lot or the less cultivated parts of a city park.
Grasshoppers, butterflies alighting now and then on the flowers, brightly marked hornets, bees busily working over the purple asters or golden rod, and many other forms hidden away on the leaves or stems of plants may be seen. If we were to select for observation some partially decayed tree, we would find it also inhabited. Beetles would be found boring through its bark and wood, while caterpillars (the young stages of butterflies or moths) are feeding on its leaves or building homes in its branches.
Everywhere above, on, and under ground may be noticed small forms of life, many of them insects. Let us first see how we would go to work to identify some of the common forms we would be likely to find on plants. Then a little later we will find out what they are doing on these plants.
[Illustration: An insect viewed from the side. Notice the head, thorax, and abdomen. What other characters do you find?]
How to tell an Insect.--A bee is a good example of the group of animals we call _insects_. If we examine its body carefully, we notice that it has three regions, a front part or _head_, a middle part called the _thorax_, and a hind portion, jointed and hairy, the _abdomen_. We cannot escape noting the fact that this insect has wings with which it flies and that it also has legs. The three pairs of legs, which are jointed and provided with tiny hooks at the end, are attached to the thorax. Two pairs of delicate wings are attached to the upper or _dorsal_ side of the thorax. The thorax and indeed the entire body, is covered with a hard shell of material similar to a cow's horn, there being no skeleton inside for the attachment of muscles. If we carefully watch the abdomen of a living bee, we notice it move up and down quite regularly. The animal is breathing through tiny breathing holes called _spiracles_, placed along the side of the thorax and abdomen. Bees also have compound eyes. Wings are not found on all insects, but all the other characters just given are marks of the great group of animals we call _insects_.
[Illustration: Part of the compound eye of an insect (highly magnified).]
Forms to be looked for on a Field Trip.--Inasmuch as there are over 360,000 different species or kinds of insects, it is evident that it would be a hopeless task for us even to think of recognizing all of them. But we can learn to recognize a few examples of the common forms that might be met on a field trip. In the fields, on grass, or on flowering plants we may count on finding members from six groups or _orders_ of insects. These may be known by the following characters.
The order _Hymenoptera_ (membrane wing) to which the bees, wasps, and ants belong is the only insect group the members of which are provided with true stings. This sting is placed in a sheath at the extreme hind end of the abdomen. Other characteristics, which show them to be insects, have been given above.
Butterflies or moths will be found hovering over flowers. They belong to the order _Lepidoptera_ (scale wings). This name is given to them because their wings are covered with tiny scales, which fit into little sockets on the wing much as shingles are placed on a roof. The dust which comes off on the fingers when one catches a butterfly is composed of these scales. The wings are always large and usually brightly colored, the legs small, and one pair is often inconspicuous. These insects may be seen to take liquid food through a long tubelike organ, called the _proboscis_, which they keep rolled up under the head when not in use. The young of the butterfly or moth are known as _caterpillars_ and feed on plants by means of a pair of hard jaws.
Grasshoppers, found almost everywhere, and crickets, black grasshopper-like insects often found under stones, belong to the order _Orthoptera_ (straight wings). Members of this group may usually be distinguished by their strong, jumping hind legs, by their chewing or biting mouth parts, and by the fact that the hind wings are folded up under the somewhat stiffer front wings.
[Illustration: Forms of life to be met on a field trip. _A_, The red-legged locust, one of the _Orthoptera_; _o_, the egg-layer, about natural size.
_B_, the honey bee, one of the _Hymenoptera_, about natural size. _C_, a bug, one of the _Hemiptera_, about natural size. _D_, a butterfly, an example of the _Lepidoptera_, slightly reduced. _E_, a house fly, an example of the _Diptera_, about twice natural size. _F_, an orb-weaving spider, about half natural size. (This is not an insect, note the number of legs.) _G_, a beetle, slightly reduced, one of the _Coleoptera_.]
Another group of insects sometimes found on flowers in the fall are flies.
They belong to the order _Diptera_ (two wings). These insects are usually rather small and have a single pair of gauzy wings. Flies are of much importance to man because certain of their number are disease carriers.
Bugs, members of the order _Hemiptera_ (half wings), have a jointed proboscis which points backward between the front legs. They are usually small and may or may not have wings.
The beetles or _Coleoptera_ (sheath wings), often mistaken for bugs by the uneducated, have the first pair of hardened wings meeting in a straight line in the middle of the back, the second pair of wings being covered by them. Beetles are frequently found on goldenrod blossoms in the fall.
Other forms of life, especially _spiders_, which have four pairs of walking legs, _centipedes_ and _millepedes_, both of which are wormlike and have many pairs of legs, may be found.
Try to discover members of the six different orders named above. Collect specimens and bring them to the laboratory for identification.
Why do Insects live on Plants?--We have found insect life abundant on living green plants, some visiting flowers, others hidden away on the stalks or leaves of the plants. Let us next try to find out _why_ insects live among and upon flowering green plants.
The Life History of the Milkweed Butterfly.--If it is possible to find on our trip some growing milkweed, we are quite likely to find hovering near, a golden brown and black butterfly, the monarch or milkweed butterfly (_Anosia plexippus_). Its body, as in all insects, is composed of three regions. The monarch frequents the milkweed in order to lay eggs there.
This she may be found doing at almost any time from June until September.
Egg and Larva.--The eggs, tiny hat-shaped dots a twentieth of an inch in length, are fastened singly to the underside of milkweed leaves. Some wonderful instinct leads the animal to deposit the eggs on the milkweed, for the young feed upon no other plant. The eggs hatch out in four or five days into rapid-growing wormlike caterpillars, each of which will shed its skin several times before it becomes full size. These caterpillars possess, in addition to the three pairs of true legs, additional pairs of _prolegs_ or caterpillar legs. The animal at this stage is known as a _larva_.
Formation of Pupa.--After a life of a few weeks at most, the caterpillar stops eating and begins to spin a tiny mat of silk upon a leaf or stem. It attaches itself to this web by the last pair of prolegs, and there hangs in the dormant stage known as the _chrysalis_ or _pupa_. This is a resting stage during which the body changes from a caterpillar to a butterfly.