exhibited by the beetles in Professor Tower's experiments, and steps are now being taken for the necessary analytical tests for the standardization of temperature effects in terms of protoplasmic activity.
Another phase of temperature effects—concerning energy release in protoplasm—has been studied by Professor Ellsworth Huntington, whose analysis of the records of piece-workers in factories established the fact that the least amount of work is accomplished with open air temperatures below the freezing point and in the neighborhood of zero Fahrenheit. The amount increases slowly, however, up to 28° F., then rapidly to 38°, slowly to 48° and more slowly to the optimum of 58° F., above which the rate and amount declines as the weather becomes warmer. It may seem a far cry from the growth of a wheat plant in California to the muscular action of a factory operative in New England, but both are directly dependent upon the fundamental characters of living matter, especially in its relation to temperature.
The distribution and grouping of organisms on the world's surface is conditioned by the agencies which participate in moving them from place to place and by the presence of conditions suitable for their survival and existence. If all species inhabited every place suitable for them, geography, so far as vegetation is concerned, would be a subject about which many closed chapters might be written. They do not, however, as they have not been carried to all the places in which they might survive, and secondly, the conditions comprising the environic complex are slowly but surely changing, reversibly or irreversibly, practically everywhere on all land surfaces. Under such conditions the dynamics of plant geography assumes an importance not yet realized.
So far we have discussed the results of analyses of our plantations and experimental settings. The geographer, however, needs to have defined for him the principles governing the variations in the various environmental components and of course temperature is an agency which has been drawn upon to account for some of the major features of distribution in geologic as well as present time. Methods and practises that have become conventionalized estimate temperatures by altitude and latitude, the actual data obtained by instrumentation being compiled as mean temperatures, and the averages of maxima and minima. I need but to refer to the measurements of temperature in terms of growth discussed previously to illustrate the inadecpiacy of these data for agricultural operations.
The obvious and popularly accepted assumption that low valleys are warm and that ridges are cold wind-swept habitats, arising from the conception of surface temperatures as in the main a function of altitude has been followed much too far, and the geographer who bases his generalizations on assumptions of this kind will be due to encounter some extremely disturbing anomalies, some of which have come in for examination and measurement at the Desert Laboratory by Dr. Shreve.
