PHYSIOLOGY OF PLANTS. HISTORY. T:p to the close of the seventeenth century nothing was known of the physiology of plants beyond the scattered impressions derived from the practical cultivation of plants in fields and gardens. in asmuch as the physiology of animals was better known, the first study of the actions of plants was an endeavor to identify plant functions with those of animals. As the functions of animals were only superficially known, this attempted identification led oftentimes to most egregious errors. But as the nature of animal functions became better known, the essential identity of the processes in both sorts of living being,: be came more evident. At first the study of phvsi ology was scarcely more than an enumeration of plant activities and their comparison with those of animals. Later, however, attempts were male to investigate the causes and conditions of the functions. For this a knowledge of anatomy was recognized as of prime importance. Deeper in sight into physiology, however. demanded knowl edge of physics and chemistry; and it was only when these two sciences underwest their pro found transformation and extension that ex planations of plant phenomena began to be pos sible. Among the earliest investigations after the revival of learning were those made in Italy by Malpighi on the movement of sap. and those of Ray on the influence of light upon the colors of plants. About the same time in Ger many Camerarius proved the necessity of pollen for the formation of fertile seeds.
Earl• in the eighteenth century Hales pub lished his studies on the movement of sap and the evaporation of water from the leaves. Later in the eighteenth century came the investigations of Koelreuter, who added to the knowledge of sexuality in plants by his experiments on hy bridization. It was in connection with these ex periments that the relations of insects to pollina tion were first pointed out. Later (1793) these interesting relations were set forth at length by Christian Konrad Sprengel, whose famous "Das entdec•kte Geheimnis der Natur" was scarce ly appreciated until the contributions of Darwin had opened the eyes and understanding of natu ralists to Sprengel's extraordinary work. About
the same time Ingenhouss showed that the green parts of plants when illuminated absorb carbon dioxide and eliminate oxygen, thus deriving the carbon which they need from the atmosphere. He also showed that the living parts of plants absorb oxygen. whether illuminated or not, and evolve carbon dioxide, thus establishing the fun damental facts of nutrition and respiration. This work was further confirmed by Senebier, who demonstrated that the decomposition of car bon dioxide takes place only in green organs. He also studied the influence of light upon the growth and green color of plants. By the be ginning of the nineteenth century Nicolas Theodore de Saussure had shown that plants not only fix carbon from carbon dioxide, but also use the elements of water, which, with the mineral salts. are a necessary part of the food materials. Between 1822 and 1832 De Saus sure and Goeppert established the connection between the respiration of plants and the de velopment of heat in their bodies. Through the influence of Liehig, about the middle of the cen tury. Ingenhouss's clear exposition of the respira tion of plants. which had been fairly established. was discarded, to be reinstated in confidence only after 1860 by the father of modern vegetable physiology. .Julius von Sachs. Yet Liebig's valuable work in connection with the chemistry of foods and food materials of plants and Bous singault's investigations in France, especially in relating the known facts to the empirical proc esses of agriculture, were of great service to both cultivators and physiologists. The year 1860 marks the rise of modern physiology. as indeed it does the rise of modern biology, many coaperat ing causes, the most notable of which was the publication of Darwin's Origin of Species, fur nishing the impulse to renewed investigation.