Lethal Environmental Factors Within the Natural Range of Growth

Perhaps no phase of theoretical biology has received more emphasis than that which deals with the interrelationships of the organism and its environment. Such themes as the "struggle for existence, " "the survival of the fittest, " "the fitness of the environment, " and "the continuous adjustment of internal rela-tions to external relations " are all rooted in this same central problem. While the vicissitudes of the environment are recognized as of utmost importance in the struggle for existence, the fact that fluctuations well within the natural range of growth of the organ-ism may prove lethal to the young of the species has not been generally recognized. The proverbial delicacy of the "hot house plant " is well known; and the common practice of "hardening" young greenhouse plants, by subjecting them to temperatures a little above the freezing point, has been shown experimentally to protect against freezing conditions which the "unhardened " plant cannot endure. So far as we are aware, however, it has not been shown that environmental fluctuations within the range necessary for growth may be fatal to plants. In the animal kingdom, a clear-cut recognition of the fact exists in the case of fish. The so-called "tempering " process, in which a change from warm to cold water is made gradually, is a common practice in hatcheries, and is supported by an abundance of experience. Scientific proof of this fact is furnished by the work of Loeb and Wasteneys (1912) on Fundulus. It was shown that fish transferred suddenly from water at 10 ° to 350C. died after a short exposure, whereas if they were changed first from 10 ° to 270C., after a few days at the latter