Not only is a belief in astrology implied throughout the _Poimandres_, but a number of separate astrological treatises are extant in whole or part under the name of Hermes Trismegistus,[1300] and he is frequently cited as an authority in other Greek astrological manuscripts.[1301] The treatises attributed to him comprise one upon general method,[1302] one on the names and powers of the twelve signs, one on astrological medicine addressed to Ammon the Egyptian,[1303] one on thunder and lightning, and some hexameters on the relation of earthquakes to the signs of the zodiac. This last is also ascribed to Orpheus.[1304] There are various allusions to and versions of tracts concerning the relation of herbs to the planets or signs of the zodiac or thirty-six decans.[1305] These treatises attribute magic virtues to plants, include a prayer to be repeated when plucking each herb, and tell how to use the astrological figures of the decans, engraved on stones, as healing amulets. [Sidenote: Hermetic works of alchemy.] Works under the name of Hermes Trismegistus are cited by Greek alchemists of the closing Roman Empire, such as Zosimus, Stephanus, and Olympiodorus, but those Hermetic treatises of alchemy which are extant are of late date and much altered.[1306] Some treatises are preserved only in Arabic; others are medieval Latin fabrications. The Greek alchemists, however, seem to have recited the mystic hymn of Hermes from the _Poimandres_.[1307] [Sidenote: Nechepso and Petosiris.] Hellenistic and Roman astrology sought to extend its roots far back into Egyptian antiquity by putting forth spurious treatises under the names, not only of Hermes Trismegistus, but also of Nechepso and Petosiris,[1308] who were regarded respectively as an Egyptian king and an Egyptian priest who had lived at least seven centuries before Christ. Indeed, they were held to be the recipients of divine revelation from Hermes and Asclepius. A lengthy astrological treatise, which Pliny[1309] is the first to cite and from a fourteenth book of which Galen[1310] mentions a magic ring of jasper engraved with a dragon and rays, seems to have appeared in their names probably at Alexandria in the Hellenistic period. Only fragments and citations ascribed to Nechepso and Petosiris are now extant.[1311] [Sidenote: Manetho.] Yet another astrological work which claims to be drawn from the secret sacred books and cryptic monuments of ancient Egypt is ascribed to Manetho. It is a compilation in verse of prognostications from the various constellations and is regarded as the work of several writers, of whom the oldest is placed in the reign of Alexander Severus in the third century.[1312] [Sidenote: The _Lithica_ of Orpheus.]