1099. Primitive surfaces affect vegetables mechanically, according to their different degrees of moveability or tenacity. In coarse sandy surfaces plants spring up easily, but many of them, which have large leaves or tall stems, are as easily blown about and destroyed. In fine, dry, sandy surfaces, plants with very delicate roots, as Protea and Erica, prosper : a similar earth, but moist in the growing season, is suited to bulbs. On clayey surfaces plants are more difficult to establish; but when established are more permanent : they are generally coarse, vigorous, and perennial in their duration. With respect to the relative proportions of the primitive earths in these surfaces, it does not appear that their influence on the distribution of plants is so great as might at first sight be imagined. Doubtless, different earths are endowed with different degrees of absorbing, retaining, and parting with moisture and heat; and these circumstances have a material effect in a state of culture, where they are comminuted and exposed to the air ; but not much in a wild or natural state, where they remain hard, firm, and covered with vegetation. The difference, with a few exceptions, is never so great but that the seeds of a plant which have been found to prosper well in one description of earth, will germinate and thrive as well in another composed of totally different earths, provided they are in a nearly similar state of mechanical division and moisture. Thus, De Candolle observes, though the box is very common on calcareous surfaces, it is found in as great quantities in such as are schistous or granitic. The chestnut grows equally well in granitic and clayey earths, in volcanic ashes, and in sand. The plants of Jura, a mountain entirely calcareous, grow equally well on the Vosges or the granitic Alps. But, though the kind or mixture of earths seems of no great consequence, yet the presence of metallic oxides and salts, as sulphates of iron or copper, or sulphur alone, or alum, or other similar substances, in a state to be soluble in water, are found to be injurious to all vegetation, of which some parts of Derbyshire and the maremmes of Tuscany (Chateauvieux, let. 8.) are striking proofs. But, excepting in these rare cases, plants grow nearly indifferently on all primitive surfaces, in the sense in which we here take these terms ; the result of which is, that earths strictly or chemically so termed have much less influence on the distribution of plants, than temperature, elevation, and moisture. Another result is, as De Candolle has well remarked, that it is often a very bad method of culture to imitate too exactly the nature of the earth in which a plant grows in its wild state.
