At this period, Olaus Celsius, first professor of divinity, whom Linnaeus afterwards, in a letter to Haller, describes as the only botanist in Sweden, returned from Stockholm, where he had been on official business, and happening to visit the college-garden, met a young man, who attracted his notice by the accurate knowledge of plants which he displayed. On inquiring after him, and receiving a satisfactory account of his character and conduct, he gave him an apartment in his house, and supplied him with every thing of which he stood in need. Thus was he on many occasions obliged, if not to solicit, at least to accept pecuniary assistance. He, however, repaid in some measure the kindness of the venerable Celsius, by assisting him in preparing his _Hierobotanicon_, in which the vegetable productions mentioned in Scripture are described. To enable him to perform his task, he was allowed the free use of a library rich in botanical works. Hitherto Tournefort was the only author to whose works Linnaeus was indebted for the more solid parts of his knowledge; but a small book of Vaillant on the structure of flowers now coming into his hands, he perceived many defects in the system he had embraced; and from the ingenious observations made by the latter writer on the sexes of plants, he conceived the idea of founding a system of botany on the stamens and pistils. With this object in view, he recommenced his studies on a new plan; the sexual distinction continually occupied his thoughts, and the knowledge which he acquired in this path became the basis of his future eminence. A small treatise which he composed on the subject of an academical disputation attracted the notice of Rudbeck, the second of the name, then professor of botany, who, being advanced in years, was looking out for an assistant. He received the ardent student into his house, and delegated to him the office of reading his lectures, and demonstrating the plants in the botanic garden. Rudbeck was also a zoologist, and had made a collection of all the Swedish birds; the examination of which failed not to add to Linnaeus's knowledge in this department of natural history. Botany, however, continued to be his favourite study; and about this period he wrote several treatises, which were afterwards published in Holland.