Their knowledge of the materia medica was acquired for the most part by experience, though there existed, previously to the time of Hippocrates, works on the virtues of plants, among which we may mention that of Cratevas. By degrees these treatises were greatly multiplied, and included, at length, a species of encyclopedia, arranged in alphabetical order;[1216] though not one single fragment of it has been spared by time. At first, and for many ages, the art relied chiefly upon simples, the qualities of which were consequently studied with great ardour, and, no doubt, with much success. Numerous individuals devoted themselves to the gathering, drying, and preserving, of medicinal roots and herbs, an occupation requiring considerable time and labour,—for which reasons the physicians, by whom it was originally performed, soon abandoned it to the rizotomists. ----- Footnote 1216: Dioscorides, however, who mentions this work, is far from speaking of the plan with praise: ἥμαρτον δὲ καὶ περὶ τὴν τάξιν· οἱ μὲν ἀσυμφύλους δυνάμεις συγκρούσαντεσ· οἱ δὲ κατὰ στοιχεῖα ἀναγράψαντες. διέζευξαν τῆς ὁμογενείας τὰ τε γένη καὶ τὰς ἐνεργείας αὐτῶν, ὡς διὰ τοῦτο ἀσυμμνημόνευτα γίνεσθαι. Proœm. p. 2. ----- But the business of collecting simples, by whomsoever performed, required great knowledge and perseverance. The individuals who carried it on spread themselves, at the proper seasons of the year, through all Greece, more especially over Mount Pelion in Thessaly, Telethra in Eubœa, Parnassos in Phocis, and the uplands of Laconia and Arcadia,[1217] making inquiries, as they went along, of the inhabitants of every district and canton respecting the medicaments in use among them, and collecting from the mouths of peasants and shepherds the fruits of their limited but close observation. They passed, as a matter of course, the greater part of their lives in the fields, studying the topography and distribution of plants, and investigating all the phenomena of vegetation. They believed, that herbs vary in virtues and powers according as they are found in mountains or in valleys, in places overrun with moisture, and where the air is rank and heavy, or on spots swelling and exposed, where they are fanned and invigorated by every breeze that blows. They laid much stress, too, on the season of the year, on the weather, and on the hour of the day; some simples requiring, it was supposed, to be gathered when the sun has exhaled from them all extraneous moisture, others before its rising, others amid the darkness of night when their leaves and flowers were suffused with dew. They were guided, likewise, in their operations by other rules, some founded on experience, others originating in fancy and superstition. In culling, for example, the thapsia[1218] and several other herbs, they were careful, having first anointed themselves with oil, to stand with their backs to the wind, persuaded that they otherwise should inhale