It is very possible, in some cases of this kind, that the soil, having been produced by aqueous agencies, may contain seeds to a considerable depth, and that their vitality may have been preserved for centuries; for we know that seeds three thousand years old, taken from Egyptian catacombs, have germinated, in favorable circumstances. In most cases of this sort, however, the winds have probably supplied the seed, it may be, long before. We were one day wandering over Mount Holyoke, where a spot recently cleared was covered with the fire-weed, a species of senecio; and as we were musing upon its origin, a strong blast of wind swept over the plants, just ready to throw off their seeds. Sustained by their light egrets, they floated away on the air in numbers sufficient to cover half the mountain with the plant, when it should be cleared and burnt over. Yet their existence would never be suspected till those circumstances should be developed. At least, until we can prove that the soil contains no seeds by the most careful examination, it will be premature to infer the equivocal production of the plants growing upon it. Vegetable physiology furnishes another fact, which seems to me to look still more favorable to this law hypothesis than the preceding, although it has not been noticed, so far as I know, by the advocates of that hypothesis. Speaking of the matter of which certain flowerless plants are composed, Dr. Lindlay says, "It is even uncertain whether this matter will produce its like, and whether it is not a mere representation of the vital principle of vegetation, capable of being called into action, either as a fungus, or algae, or lichen, according to the particular conditions of heat, light, and moisture, and the medium in which it is placed; producing fungi upon dead or putrid organic beings, lichens upon living vegetables, earth, or stones, and algae where water is the medium in which it is developed." Again, in speaking of that green slime which often covers the soil, rocks, walls, and glass in damp places, he says, "The slime resembles a layer of albumen, spread with a brush; it exfoliates in drying, and finally becomes visible by the manner in which it colors green or deep brown. One might call it a provisional creation, waiting to be organized, and then assuming different forms according to the nature of the corpuscles which penetrate it, or develop among it. It may further be said to be the origin of two very distinct existences, the one certainly animal, the other purely vegetable."--_Natural System_, pp. 326, 328, 334.