But it must not be supposed that the importance of Sachs' discovery, and the rapid consequent extensions of our knowledge, did their work forthwith in disabusing men's minds of old and erroneous notions. To say nothing of numerous smaller misconceptions which still held their ground owing to the stupendous ignorance of plant-physiology which prevailed, we find incompetent teachers and text-books were still propagating ideas worthy of ancient times. The confusion between oxygen-respiration and the gas interchanges in carbon-assimilation was by no means eliminated even recently, though it can no longer withstand the deliberate onslaughts now made on it. That the roots take up food as such from the soil, and that that food is directly employed by the plant for its nutrition is even yet implied in daily conversation around us; and although matters have advanced so far that everyone now knows that the substances at the roots must be in solution, ere they can be received into the plant, it sometimes leads to astonishing replies, if we press the question very far as to how the absorption takes place, in an elementary examination of agricultural students. That manures are foods to the plant, that sap circulates, that transpiration is of use to keep the plant cool, and wood is a "porous body," etc., are only a few of the misconceptions still current, in a decade that has found publishers for a work advocating that roots are congealed sap, and that the leaves of plants absorb the moisture and dust of the air, and so provide the plant with food, and for a paper explaining the action of root-hairs as tubes with open pores at their tips. But the gravest misapprehensions current among us are due to the crude ideas as to what a plant really is: this, I take it, is owing to the difficulty of grasping what physiologists mean by organised structure, and leads to regarding the living being either as a mere aggregation of chemical compounds, built up by the ordinary play of chemical forces, as we know them, acting on dead matter, or, as in the days before organic chemistry, as a mysterious entity endowed with "vital force," and with properties not amenable to scientific investigation. The mistaken notions as to the powers of roots to "select" those substances which the plant requires, and to reject useless ones was merely an expression of this belief.