“Now let us see how the plant is nourished by the various substances of which we have just studied the most important. Every form of plant-life is made up, not of a compact and uniform mass of matter with no occasional empty spaces, but, on the contrary, with the aid of a microscope it is seen that an infinite number of very minute cavities called cells are interspersed throughout the body of the plant. These cells may be regarded as extremely small closed sacs, sometimes round, sometimes oval, but more often with irregular and angular outlines by reason of the mutual pressure exerted by the cells. The cell-wall is composed of an excessively fine membrane. In the pith of the elder, all riddled like a sponge, you have an example of cells large enough to be seen without a microscope. Other cavities are long, pointed at both ends and swollen in the middle like a spindle. They are called fibers. Still others form canals of uniform size throughout, as fine as a hair and long enough to extend from the roots to the topmost leaves. These canals are called ducts. Look closely at the cross-section of a very dry vine-branch, and you will see a multitude of orifices into which it would be possible to thrust a hair. Those are the openings into so many broken ducts. Everything in the plant, absolutely everything—root, stalk, wood, bark, leaves, flowers, fruit, seeds, no matter what—is composed of a mass of cells, fibers, and ducts. “That understood, let us consider the root of the plant. In its new parts, at the tip-ends of its finest ramifications, tip-ends that we have called spongioles, it is composed of cells just formed and consequently tender and fitted for absorbing easily the moisture in the soil. Spongioles, then, fill themselves much as sponges would do. That done, conduits offer their services for conveying the liquid to the top of the plant: they are the ducts just referred to, and comparable here to the water-pipes in our own fountains. But if in fountains water runs by its own weight, going from the highest to the lowest point, it is not so with the liquid absorbed by the roots, a liquid running from below upward. What then is the force that makes it ascend?