His catalogues of the plants collected by those associated with various expeditions, his Kew lists (which were published under Aiton's name) are well known to students of systematic Botany, but his fine monograph on _Rafflesia_, containing, as it does, many observations of general interest will well repay perusal even after these many years. His studies on Cephalotus, on Caulophyllum (with its remarkable seed formation), as well as his considerable memoir on the Proteaceae, shew him as a naturalist imbued with keen insight and possessed of extraordinarily sound judgment. But Brown did not confine his attention to phanerogams, but, as might have been anticipated from the studies of his earlier years, pursued his investigations into the little explored field of the cryptogams. We have seen that as a young man he had been greatly attracted to the study of mosses. Later on he contributed two important papers on these plants to the Linnean Society, one in 1809, in which he described two new genera, one of them Dawsonia, the other Leptostomum, both from Australasia. The introductory remarks in which he discusses the character of the moss capsule, are interesting as shewing how hopelessly impossible it was at that time to arrive at a scientific understanding of its structure, so long as everything was tested by the touchstone of the flowering plants. Ten years afterwards he reverted to the same subject, describing the new genus _Lyellia_ from Nepaul, and comparing it, as was his wont, with allied genera, e.g. Polytrichum, Buxbaumia and many others, with the view of elucidating the significance of its structure. The spores, however, are still spoken of as seeds. The male plant is generally regarded as the _barren_ plant. It is not easy to reconcile the existence of male flowers with the view of Beauvois which Brown seemed still to consider as not disproved, viz. that the seeds and pollen were both contained in the capsule. Mosses were not the only cryptograms to which he turned his attention. He described a new species of Azolla (_A. pinnata_) from Port Jackson, and the plant was illustrated by the excellent drawings of Bauer. But here, too, the time was not yet ripe for a morphological understanding of the structure. The megasporangium was thought to be the _male_ flower, the microsporangia being interpreted as capsules containing several seeds (the glochidia). The explanation of the supposed male flower presented difficulties, but he states that the lower cell (i.e. the megaspore) was once found filled with a powder replacing the turbid fluid ordinarily occurring there, and the powder was supposed in some way to be ejected and thence to be conveyed to the female organ. Ferns also claimed his attention, and among his other contributions he founded the genus _Woodsia_, calling attention to the character of the involucrum (indusium), which separated it from the other polypodia with which the species had previously been associated.