3 So too in the case of plants: their species will be formed, not from a simple element, but by a process of composition, just as saltness and the substance of sand are formed in[1] the water of the sea. For vapours which rise, when they become solidified, will be able to conceive these plants, and the air will descend and bedew the ground, and from it will come forth the form of their seeds through the powerful influence of the stars. But plants must necessarily have some material, and this material is water. There are, however, different kinds of water, and water only rises if it is fresh, and salt water is heavier than fresh; and so that which rises above water is rarer than water. When, therefore, the air draws it up, it will become rarefied and rise still higher; and this is why fountains and streams are formed in mountains. Similarly phlegm and blood rise to the brain, and all foods[2] also rise; so too all water rises. Even salt water rises in that part of it which heat dries out into the element of air, and, because air is always higher than water, that which rises from salt water is fresh. We shall often find the same thing taking place in baths. When heat takes hold of salt water, its parts will be rarefied, and vapour will rise in a contrary direction to the depth of the bath, and the particles of salt and the natural moisture become separated, for the latter is of the nature of air and follows the vapour; and cloud after cloud of vapour rises upwards, and when they reach the top of the room they press upon one another. The vapour will thus collect and become condensed, and will turn into drops of fresh water dripping down, and so in salt baths the vapour will always be fresh.
Plants ought not to grow in salt water, on account of its low temperature and dryness. This means that the plant lacks two things—its proper material and a position suitable to its nature;[3] when these two conditions are present a plant will grow. Now we find that snow is the substance furthest removed from an equable temperature,
