in the cellar and one in the field is known to every farmer. Recently it has been found that some plants from warm regions where the days are short and which did not produce seed in the north could be made to set seed by the simple device of covering them and thus shortening the hours of exposure to light. There is reason to believe that the barring of feathers as seen in many birds may be due to differences of growth as between day and night.

Influence of Wind

The winds, also, have some influence on the distribution of life. They greatly increase the evaporation of water and thus affect the humidity of the air and the condition of the soil. They cause more rapid conduction of the heat from the bodies of animals and thus render them more sensible to lower temperatures, or cause pleasant sensations if the temperature is high. To some extent they influence the distribution of such light animals as butterflies and moths which find difficulty in traveling against the wind. The gypsy moth has traveled northeast from the infection center in eastern Massachusetts more rapidly than it has gone southwest. Any one who has seen the streets of a mid-west city covered with the lint of the cottonwood tree will appreciate the action of the wind. Exposure to or protection from various winds decidedly affects the value of land for agriculture. Farmers in Nebraska have often seen a promising field of corn or oats ruined in a day by a hot wind from the south. Animals are affected as well for some hide when the wind blows. Man himself is not immune. We need not stop to discuss the damage done by tornadoes nor list the benefits of the trade winds. The winds as bearers of the rain clouds have proved their worth to man.

Again we must remind ourselves that in nature all these factors are operating all the time and in reality cannot be separated. Moisture must be considered in connection with temperature, or altitude, or prevailing wind. A moist tropical valley, sheltered from the wind, may be very unhealthful for man owing to the abundance of the lower forms of life, while a similar situation in other zones may be most desirable. "In times of calm, the air temperature may itself be quite unimportant. An unobstructed exposure to solar radiation, combined with a calm condition of the atmosphere makes it possible for certain high valleys in the Alps, which are especially well sheltered, to rival many southern winter resorts, notwithstanding the extreme cold of the winters." 18 In California the Napa Valley north of San Francisco produces some of the earliest fruit for similar reasons.

Let us take one last glance at these cosmic factors. The air contains an enormous amount of dust of many sorts. Much of this will find its way to earth anyhow, but the washing of the air by the rain is one of the real services nature affords. How differently the air smells after a refreshing rain, and how all nature, man included, seems to rejoice! That much of this dust, often poisonous, is man made is another story. The presence of ozone indicates the absence of organic impurities, and ozone is not to be found in inhabited rooms. It is four times as common in the Alps as in Paris. To keep the air fit to breathe may be one of man's problems in the future just as the keeping of the water fit to drink is a major problem to-day.

ORGANIC ACTIVITY

The activities of an organism depend on its structure and its response to a stimulus just as iron responds to the presence of oxygen. The bacteria respond to certain stimuli. Drop some salt in a solution containing certain bacteria and they will get as far away from it as possible. Look at the bacteria in the spectrum of a drop of water and they will be found concentrating in the red and yellow sections. They do certain things because of what they are and not because they have any theory as to what they should do. In so far as we know, to mankind alone is reserved the common desire to be something else, as the housewife looks at the cat and wishes that she could trade places. Within very narrow limits the bacteria may move and change their adjustment. Plants cannot, they must live or perish as conditions permit. Animals readjust when possible by movement; in the higher forms by changing habits, yet most of their adjustment to the environment is not self-determined.

Animals must breathe oxygen. The available supply is in the air or in the water. The fish does not decompose the water but utilizes the free oxygen it carries. It cannot live in the air any more than man can live in an atmosphere of pure oxygen. We say, then, that the fish is adapted to his environment, which means that being what it is it must live under certain conditions. Brook trout thrive if there are 5.5 c.c. of oxygen to the liter of water but are driven out by the same amount of carbon dioxide. Plants, on the contrary, flourish if the carbon is present. In an aquarium there is often an excess of nitrogen which is harmful to the fish. The whales and porpoises being air-breathing animals must come to the surface. Yet the whale would soon perish in the air regardless of its food supply, for the thick fat which protects it in water would be fatal under the rays of the

sun.

Water and air contain elements both good and bad from the standpoint of animals. Few plants or animals accustomed to fresh water can survive in the ocean and Great Salt Lake is almost devoid of life. If the streams are polluted with acids, or the refuse of mills and towns, the fish soon leave or are killed. The fumes from a smelter may destroy the vegetation for miles. Butte, Montana, once bore the reputation of having neither lawns nor trees. Stone cutters, coalminers, men who work in the dust of the streets, breathe in so much foreign matter that their lungs are coated, and they are made susceptible to the attacks of germ diseases if not actually poisoned by the dust inhaled if it contains lead or phosphorus.

Movement is determined by structure. The fish swims not from choice but from necessity. The plant grows towards the light and perishes if the light fails. The animal finding itself in a disagreeable situation may swim, run, or fly, as the case may be, to seek other conditions. If it fails, it may perish; if it succeeds, all is well. Complete self-realization, even for man himself, depends on the maintenance of adaptation.

"If animals are placed in situations where a number of conditions are equally available, they will almost always be found living or staying most of the time in one of the places. The only reason to be assigned to this unequal or local distribution of the animals is that they are not in physiological equilibrium in all the places." 19 Their habitat then is selected by "trial and error," that is, if they do not feel comfortable in one place they seek another. Animals of the same species show different habits in different environments and there is a vast difference in the habits of species. "Animals living in the same places, and apparently under the same external conditions of existence, nevertheless behave in quite different ways under the influence of the various substances held in solution by the water, as salt, oxygen, carbonic acid, etc. The ova of different and yet very closely related forms can endure a long period of drought, or even require it to enable them to develop. Hence, every change, as for instance, in the composition of the water of a lake or river will not affect the fauna inhabiting it equally, but will act on some individuals ; some will bear the change without being in any way affected by it, others will die, while others again will survive." 20

Adaptation, then, is essential if the individual or the species is to survive. Yet the conditions of the world are ever varying. "The animal lives in an environment which is constantly changing. Its spontaneous movements are constantly bringing it into different conditions. It tends to regulate its internal processes by selecting the point in the environment in which its internal processes are not disturbed." 21 There are several types of adaptation to meet the daily demands.

DANGERS OF CHANGES

Sudden changes are the most dangerous. The frost kills both plants and insects; the hot wave destroys the corn. Against such disasters life has little defense. The changes which come with the seasons finds nature fertile in inventions and prepared. By means of seeds or buds which remain dormant plant life survives the winter or drought. The insects lay eggs or sleep in larval form. Birds migrate to find new sources of food. Bears hibernate.

There are physiological changes as well as changes in habits. A frog is lively in warm water but becomes sluggish and drowsy as the temperature falls. The blood temperature of hibernating rodents falls to about 40° sometimes nearly 35°. A little oxygen reaches them but they require so little that immersion for an hour in carbon dioxide will not kill them. They must be fat when they begin the long sleep and must waken gradually. It is believed that if their temperature falls too low they awaken automatically, and by movement and the inhalation of oxygen again raise their temperature.

Even the daily changes are significant. Sleep seems to result from a drugging of the system by the carbon dioxide and other substances produced by everyday activity which are less rapidly eliminated. At night, therefore, the eliminating process goes on until a balance is secured again.

Readaptation by change of habits is common among animals and we may say that it is due to their education. Our common chimney swifts formerly nested in hollow trees or crevices in the rocks but have accepted the chimneys as substitutes. Wrens and martins appreciate the houses built