_Extremes of Temperature are Most Important._—It is, on the contrary, rather the _extremes_ of temperature, more particularly of cold, but frequently also of heat, together with the total amount of heat available during the growing season, that determines such adaptation so far as temperature is concerned; for no culture plant can be successfully grown where the temperature during winter even occasionally falls for more than a few hours below the point which it can resist; and for each plant there is a certain aggregate requirement of heat to carry it from germination to fruiting. Even different varieties of one and the same plant differ materially in the latter respect, so that it is very important that in the selection of varieties to be grown, this factor should be taken into consideration. It cannot be too strongly urged that the comparison of annual means of temperature, so commonly made by promoters of colonization schemes, must not be taken as a guide either in the estimate of cultures in which the immigrant may desire to engage, or by those in search of a climate adapted to their health-conditions. _Seasonal and Monthly Means._—The statement of the mean temperatures of the conventional four seasons—spring, summer, autumn and winter—afford a much clearer conception of climatic adaptations; provided always that the extreme temperatures be considered at the same time. With the same understanding, the monthly means are still more instructive; but here again, it is most essential that the distribution and amount of rainfall in each be regarded at the same time, since the most desirable temperature is of no avail without the moisture required for vegetation. In some cases, _e. g._, that of California, it becomes necessary for practical purposes to regard the “season,” and not the calendar year, as the unit or reference for crop production. There the crops depend upon what rainfall may occur from October to May, there being no summer rains of agricultural significance, and outside of irrigated lands, almost all vegetation save that of trees being in abeyance. In India, there are two distinct growing seasons (“kharif” and “rabi”), corresponding to the two “monsoon” seasons; and no matter how much rain may fall during _one_, almost total failure may occur in other tropical and arid sections of that country. The _Daily Variations_ are of interest chiefly with respect to health conditions, since most plants are more adaptable in this respect than the average man. RAINFALL.