JOHN, a botanist of great eminence, was born at Cronstadt in Transylvania, in October 1739, of an originally Saxon family. In his earliest years he discovered a strong attachment to the study of botany, in which he afterwards excelled so much. He was left with very little to support him on the death of his father. The fame of Gerlach led him to Zittau in Lusatia, where he prosecuted his studies for three years, assisted by the generosity of different benefactors. He studied philosophy, mathematics, and medicine, at Leipzig, where he was distinguished for his diligence and regularity of deportment. He afterwards assisted Ludwig in the regulation of his library, anatomical museum and botanical garden; and in 1756, he entered into the family of Bose, professor of botany, for whom he prepared plants for demonstration, and attended patients in the public infirmary. In 1759 he took the degree of M.D. and practised at Chemnitz in Saxony, where he entered into the married state.

It was customary with him to walk the fields by five in the morning, to contemplate the beauties of nature, to visit his patients after breakfast, and spend the afternoon and evening in examining such plants as he had collected during his early excursions. He particularly applied himself to the investigation of the grasses, and indeed of the whole cryptogamia class of plants, which botanists at that period had greatly neglected. At the age of 40, he taught himself to draw and paint the objects which he had discovered, and the compound microscope which he received from Koehler of Dresden, greatly assisted him in those researches. By the persuasion of his second wife (whom he married about a year after the death of his first), he was prevailed with to settle at Leipzig in 1781, where he published his great work, entitled, Fundamentum Historiae Naturalis Muscorum Frondosorum. In this he gave an accurate history of mosses from his own observations, and illustrated the whole with appropriate plates. In it he discovered such sagacity, industry, and profound research, as astonished all the botanists of his time, and induced them to pay more attention to this curious subject. He gained the prize given by the Peterburgh academy for his curious and excellent treatise Theoria Generationis et Fructificationis Plantarum Cryptogamicarum Linnei, mere propriis Observationibus et Experimentis Superstitiva, published in 1784.

His literary reputation increased his medical practice; he was chosen physician to the town guards in the last mentioned year, and two years after he became professor of medicine in the university. In 1789, he was chosen ordinary professor of botany, and superintended the physic garden. He corrected the false notions which then prevailed, respecting the efficacy of the medulla or pith, the perforation of the flowers, the excrements of plants, the increase of the vessels of vegetables, and the genuine use of the leaves. By the death of a favourite daughter of a consumption at 16 years of age, he received a severe shock; and a catarrhal affection, followed by a nervous fever, deprived the world of that great man on 7th of February 1799, in the 66th year of his age.

It is agreed on all hands, that Dr Hedwig was a man of great modesty, the usual concomitant of extraordinary talents; that he was friendly and benevolent, upright in his dealings, not solicitous about wealth, and free from parade, both in teaching and in writing. In the forests of Hispaniola there is an ever-green tree, the name of which, Hedwigia balsamifera, was intended in the most honourable manner to perpetuate his memory. He left behind him two sons, one a painter of eminence at Magdeburg, and the other Dr Romanus Adolphus Hedwig, already known to the botanical world by several publications.