THIS work, the joint production of the late Prof. Lorentz and of Mr. G. Niederlein, is a substantial addition to our knowledge of the vegetation of one of the least explored portions of the earth. It forms one portion of the scientific results of the expedition into Patagonia conducted in 1879 by General Roca, who has since been elected President of the Argentine Confederation. The Indians who, under the vigorous and stern administration of General Rosas, had been terrified into inaction, if not into submission, gradually took courage when they had to deal with less energetic opponents. At repeated intervals the wandering tribes, especially those of Arau-canian stock, made destructive incursions through North Patagonia and the south of the province of Buenos Ayres, massacring the white settlers and driving off the cattle. It had long been the declared policy of the Argentine Government to confine the Indians to the region south of the Rio Negro, by establishing military posts at suitable points in the valley of that river; and to carry out this project was the object of General Roca's expedition. The chief station occupied was Choloechel, a large island inclosed by two arms of the Rio Negro. From thence the upper valley of that river was followed to its junction with a large tributary, the Nauquem. Prof. Lorentz had already returned to Buenos Ayres, while Mr. Niederlein travelled northward to Mendoza. Although the expedition was carried out at an unfavourable season—the autumn and early winter of the southern hemisphere—the authors succeeded in collecting 337 species, of which thirteen are ferns and the remainder flowering plants, in a district which includes only the north-western portion of Patagonia. It is not, however, easy to say how many of the numerous species not hitherto recorded as natives of Patagonia are henceforward to be added to its scanty flora. Many of the species recorded were found in the region lying north of the Rio Colorado, which is generally regarded as the northern boundary of Patagonia, and are not said to spread to the south of that river. Again, as many as sixty-five species of flowering plants were collected in such an imperfect condition that the authors have not been able to assign to them specific names, and many of these will doubtless be found identical with those already known as natives of the country. Further, it must be added that, of twenty plants described as new species, several appear to rest upon slight distinctive characters, which, in the eyes of many experienced botanists, will entitle them to be counted rather as varieties than as altogether new species.