sidedness of the perceptions of chemical analysis, which drew conclusions as to the soil nourishment for vegetation only by comparing soil analysis with plant analysis, could only yield a one-sided solution of the question at issue, particularly that of plant nutrition. Not until synthetical research as to the nutrition of plants made upon living specimens could it be determined on the side of the plant what elements taken up from the soil serve for food, what of the material taken up is used for other purposes, and what is merely neutral. Thus agricultural chemistry, under the influence of plant physiology, has become transformed into agricultural physiology, which to-day is to be counted one of the most important studies that contribute to practical life.
The fruitful cooperation of scientific learning and of agriculture and industry may be illustrated by the following instructive example: Long before Liebig's time the farmer knew that the cultivation of leguminous crops would make the soil richer in nitrogen, in that nitrogen compounds accumulate that which can be assimilated by plants. It was also known that leguminous plants produce peculiar little tubercles on their roots, which were explained in most varied and circumstantial ways. Bacteriological investigation has shown that these tubercles constitute the habitat of certain bacteria, which obtain entrance into the roots of leguminous plants, and live there in the mutually helpful relation of symbiosis. These bacteria, which live in peas, lentils, lupines, etc., possess the remarkable capacity of bringing the nitrogen of the air contained in soil into compounds which can be assimilated by plants. Thus the old riddle was solved. If beans be planted in sterilized soil they grow less vigorously than in ordinary soil, which harbors the bacteria in question. Abundance of these peculiar bacteria in the soil increases the productiveness of leguminous crops. This knowledge has resulted in a new industry. In the famous dyeworks of Meister & Lucius, in Hochst, is generated a product called "nitragin" for the cultivation of lupines, peas, and other legumes. This "nitragin" is simply artificially increased bacteria of different species kept in the resting stage, which, added to the soil in which lupines, etc., are planted, increases the available nitrogen supply.
Similarly numerous other sciences were richly repaid in practical help by plant physiology for what they had first furnished for "working capital" in the form of knowledge and stimulus. Therein, however, the account between theory and practice is not settled. That great account will, indeed, never be canceled. With the advancement of agriculture, of commerce and industry, arise continually scientific problems, and new scientific learning and discoveries ceaselessly promote practice. Ever more and more is disappearing the old opposition between science and practice, and more and more the opinion matures that human progress rests upon the harmonious cooperation of both.
The invasion into the realm of practical life by plant physiology has
