days a year. On the North Pacific coast 65 per cent of the days are cloudy; in the region of the Great Lakes, 50 per cent; Mississippi and Missouri valleys, 45 to 50 per cent; while Arizona and New Mexico have one of the sunniest climates on earth, only 30 per cent of the days being cloudy. Corresponding to this is the rainfall. On the North Pacific coast the rainfall is estimated at 60 to 100 inches annually; in the region of the Great Lakes, 30 to 40 inches; lower Mississippi Valley, 45 to 60 inches; upper Mississippi and Missouri valleys, 15 to 40 inches; Arizona and New Mexico, 10 to 20 inches and Eastern coastal plain, 40 to 60 inches.

Inasmuch as all life depends upon water, the question of rainfall is one of extreme importance. The annual average of seven to ten inches makes general agriculture possible, provided that the rain comes at the right time. A much heavier rainfall coming in a brief period 'followed by a long drought may prohibit the growth of plants. If the rains are light, the water may evaporate ere plant roots are benefited; if very heavy, they may beat down and destroy crops and wash the soil. Fog may bring little precipitation, but may produce many of the same effects and be very helpful, while dew prevents freezing ofttimes and also furnishes moisture. Granted then an adequate rainfall, under given conditions, an increase may produce greater results as this chart shows: Relation Between Annual Rainfall and Number of Sheep per Square Mile in Australia and Argentina

In the wheat districts the added yield was almost exactly the same as difference in inches of rain:

1 acre inch water will produce 21⁄2 bu. wheat 10 acre inch water will produce 25 bu. wheat 15 acre inch water will produce 371⁄2 bu. wheat 20 acre inch water will produce 50 bu. wheat?

The total reduction in the corn crop of the United States in 1913 owing to the drought of that year was estimated at 750,000,000 bushels. In one place in Kansas the thermometer stood at 100° or over for 64 days, while the total rainfall between July 1 and September 7 was 0.03 inches.

In Jamaica with 56 inches of rain, sugar yielded 1,441 casks per acre; with 76 inches, 1,559.8

In marine climates wheat is said to contain 9 to 12 per cent of protein, while in Russia and Hungary it is 4 to 8 per cent richer. Hot, dry climate decreases the proportion of starch and increases that of gluten."

Moist tropical valleys sheltered from the wind may be very unhealthful owing to the growth of lower forms of life. A similar situation in other zones may give happy results. "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 6 HANN, J. o. c., p. 58.

7 BAILEY, L. H. Farm and Garden Rule Book, p. 34.

8 HANN, J. o. c., p. 58.

9 Ibid., p. 141.

many southern winter resorts, notwithstanding the extreme cold of the winters." 10 In California the Napa Valley north of San Francisco produces some of the earliest fruit for like reasons.

In damp climates the water in the air forms nearly 3 per cent of the whole by volume while in Central Europe the percentage is only 1.3. The percentage of carbon increases during fogs. Air ordinarily contains many impurities, both inorganic and organic. In a cubic meter of air in the Alps one observer found 345 bacteria per cubic meter, whereas in Paris 4,790 were found. One of the great services performed by rain is the cleansing of the air by removing these impurities. The air of the desert and the ocean is very pure. The presence of ozone indicates the absence of organic impurities, and ozone is not to be found in inhabited rooms. In the Alps it is found to be four times as common as in Paris. Hann shows the extent of the contamination of the air in cities by the following table:

Impurities in Air, Feb., 1891. Greenhouses at Chelsea and Kew Deposits Equal to 22 Lbs. per Acre, or 6 Tons to Mile 11

The soot deposit each year in central London is esti

mated at 426 tons per square mile; in Leeds at 539; in

10 HANN, J. o. c., p. 38.

11 Ibid., p. 77.

Glasgow at 820 and in Pittsburgh at from 595 to 1940. The smoke at Pittsburgh contains about 3,000,000 tons of sulphur yearly or enough to dissolve 265,000 tons of structural iron. The damage done is estimated at $10,000,000. The city of Los Angeles gets from 60 to 75 per cent of all possible sunshine, while Pittsburgh gets from 35 to 58 per cent.

It is quite as necessary for the florist to control the moisture as the temperature if he would grow plants under glass. Some plants demand much more moisture than others. This fact gives humidity some of its most important indirect effects. In a given locality an excess of rain above the average may promote the growth of poisonous plants. In Montana the stockmen have long realized the increased frequency of trouble due to the larkspurs, water hemlock, loco weeds, and poison camas. Excess moisture is very likely to lead to epidemics of disease because of the fact that under such conditions the plants or animals causing disease and the types carrying the disease flourish. In Africa the sleeping sickness is carried by the tsetse fly inhabiting the banks of streams and ponds. Malaria disappears in the Middle West when the marshes are drained and the land cultivated. Indeed, the disappearance of the great hordes of horses that once inhabited North America long before the advent of man is best explained on the basis of some disease; and it is interesting to note that fossil flies similar to the diseasecarrying flies of Africa (glossina) have been found. In other words, moderately dry conditions have always been most favorable to the higher types of life. "It is a matter of universal observation that in tick or insectinfested countries dry seasons result in the reduction, moist seasons in the increase of diseases; dry localities

are favorable, moist localities are unfavorable." 12 Perhaps the plagues of history occurred during wet seasons. With reference to increased rainfall, Osborn further says: (1) It may diminish the supply of harder grasses to which certain quadrupeds have become thoroughly adapted; (2) it may at the same time produce new poisonous or deleterious plants; (3) it may be the means of introducing new insects or other pests, and new insect barriers; (4) it may be the means of introducing new protozoan diseases and new carriers of disease; and (5) it may be the means of erecting new forest barriers to migration, or new forest migration tracts for certain carnivora, such as the bears." The last clauses call attention to the fact that migration is facilitated or made impossible by the presence or absence of cover, of food supply, of dangerous animals or insects.

Moisture in the form of snow is not to be overlooked. Radiation from snow lowers the temperature in winter and retards its rise in spring, hence April is colder than November. Snow may blanket the earth and afford protection to seeds, bulbs and roots which would otherwise perish from the cold. This protection is likewise extended to animals, even to man himself. Snow houses are not undervalued by the Eskimo. Snow, on the other hand, may cover the grass and make it impossible for the animals to get food. Horses will get at the grass under three feet of snow and survive, while the cattle perish. The snow may cover the ordinary food supply and force animals to eat twigs or taller plants which may be indigestible or even poisonous. Again, the snow may make traveling difficult for certain types and thus favor their enemies. The deer 12 OSBORN, H. F. Age of Mammals, p. 508.