deal with a whole series of questions in osmotics from the standpoint of pure physics. As a result, an insight was attained by which the significance and explanation of numerous processes in plant life could be arrived at. Moreover, the experiments of this plant physiologist formed the foundation upon which was built the now famous Van't Hoff's theory of osmotic pressure, which, according to this theory, comes about in a way analogous to that of gas pressure. This is not the first time that plant physiologists have taken up the question with helpful results in the theory of osmosis. The genial and many sided Dutrochet, the discoverer of "exosmosis and endosmosis," was in the front rank of plant physiologists.
As with chemistry and physics, plant physiology stands also in this relation of reciprocal exchange with meteorology and climatology. How greatly plant life is affected by meteorological conditions and how the distribution of vegetation is dependent upon climate is evident every- where, and rich is the knowledge which plant physiologists have gained by the application of the teachings of these two sciences. But in certain investigations relating to the life processes of plants these teachings did not suffice, and so, on the part of plant physiologists, many climatological and meteorological questions had to be taken in hand. For example, one physiologist, in order to learn the mechanical effect of rain, i.e., to find out the exact force of large rain drops on leaves, determined the weight of the heaviest rain drops, the velocity of fall, and the working force of falling rain. Likewise, contributions to a more exact knowledge of the importance and significance of light to plant life were made by plant physiologists.
The connection between science and life has never been so conspicuous as now at the turning of this century, and will doubtless become yet more striking in the next century. Proud overbearance on the one hand and a capacity for misunderstanding on the other have often and for a long time maintained a sharp antagonism between science and practical life, which rested with both sides on insufficiency of knowledge and narrowness of view. Really great investigators always recognize that, as Helmholtz opportunely expressed it, knowledge alone is not the end of mankind upon the earth, but that knowledge should be applied in the affairs of practical life. Only in this sense is knowledge power, as Helmholtz thoughtfully added on the same occasion.
The great botanical reformer, Schleiden, declared in the middle of the century to his fellow-botanists, who absolutely disregarded the application of botany in practical affairs: "All the industries which make use of vegetable stuffs in manufacturing, etc., in doubtful cases ask in vain of botany for information, although it is in a position to direct and advise the industries, but it has no practical knowledge to give; knows least, often, the very plants which furnish the most important stuffs, and borrows even from artisans themselves every-
