THE POPULAR SCIENCE MONTHLY.
themselves when only the 'good beasts' are selected to lie together."
Play and Development.—In a paper on play as a factor in development, published in the American Physical Review for December, 1897, George A. Fitz, of Harvard University, places himself upon the theory now generally accepted by those who have given the most careful study of the subject, that play is simply the most important means Nature has of preparing her children for their life work. "We can readily see how this has come about. The animals which played were able to make a better fight for existence, hence survived, and fixed in their progeny the desire to play as an instinct. Play is not merely the result of the accidental desires of the individual; it is a result of that natural selection which demands everything serviceable to the preservation of the species. Thus youth becomes more completely an apprenticeship to life, with play as the master workman. All of Nature's children play and are thereby prepared to live; not playing, they die. Granting, then, that play is one of the most powerful instincts in animal life, let us study its more intimate relations to human life. How does the child who plays vigorously and spontaneously differ from the child who plays under close restriction or not at all?. . . He is born with an inherited tendency to grow into the adult form, but this inherited force toward development is not sufficiently strong to produce unassisted more than a mimicry of the best adult form, mental or physical. The great law of development is the law of use. No organ or tissue, no power of muscle or brain, can be fully developed except through use, through effort. In the play of young animals we find all the conditions of use necessary for their highest development. In the spontaneous play of the child with unrestricted opportunities, we find again the conditions of use for all the tissues fully satisfied." Further than this, the child is habituated to make rapid judgments in the presence of ever-changing relations; there is probably no factor so potent in the balance of the nervous system; in its psychic effects it gives a complete psycho-physiological picture of pleasure. "In play, the child is the unit of force; he initiates his own conditions. His limitations are self-imposed. His self-control lies in execution rather than inhibition. He is concerned with self expression rather than with self-repression. Play thus relates itself to the truest conception of education, the development of power, the power of the individual to act as a self-directed unit in civilization. The self-control gained by play acts immediately, strongly, and honestly in response to conditions as they are presented in life."
The Place of Plant Physiology.—Plant physiology, as briefly defined by Prof. D. T. MacDougal, is concerned with the fundamental properties of the protoplasm of plants, and the functions of the organisms into which it is formed. It therefore includes the consideration of all reactions of growth, movement, metabolism, changes in form, instability, and other phenomena resulting from the activity of forces internal to the plant. It merges into morphology on one side, and partly underlies oölogy on the other, and with bacteriology and mycology forms the basis of the study of pathology. Physiology and chemistry join in the consideration of the chemical activities and products of the organism, and the principles of physics are involved in the investigation of the plant machine. It is too often slighted in schools by being made a text-book and routine study. "A systematic survey reveals the fact that, instead of a complete and thorough plotting of the great field of physiology, we have made here and there a few simple trails through the dense jungle of ungrouped and vaguely defined principles, and the greater part of the work is yet to be accomplished. The fundamental problem of the constitution of living matter still confronts us." We have not yet succeeded in interpreting clearly even the cruder visible phenomena of the cell. The interprotoplastic threads have so far received no conclusive interpretation. Numerous problems relating to nutrition wait for solution—the relations of chlorophyll, of the nitro-bacteria, the acquisition of nitrogen, the balance and combined action of the mineral elements in the soil, the formation and work of the alkaloids, glucosides, pigments, and other compounds in the plant, and the ascent of sap, are only a part of the subjects concerning which we are still in the