PHYTOGEOGRAPHY still presents many difficult problems, the final solution of some of which is extremely unlikely, though patient research will doubtless bring us much nearer the truth than we have yet reached. The latest comprehensive work on the subject (Grisebach's “Vegetation der Erde”) is a very good exposition of the existing distribution of plants, but it is nothing more. Since the promulgation of the theory of descent, however, the study of the dispersion of plants has entered upon a fresh phase, and it has received the attention of some of the ablest minds engaged in botanical pursuits; and with the ever-increasing geological evidence of the composition of the floras of former periods there is a good prospect of a real advance in this branch of science. Unfortunately there is a tendency to travel far beyond a point warranted by the evidence. This remark specially applies to the determination of many of the fossils of the earliest Tertiary times. Whether fresh discoveries will prove the correctness or the incorrectness of Unger's “New Holland in Europe,” we do not venture to predict, though we think the latter; but we agree with Saporta that most of the assumed determinations are better designated by such terms as affiliation and collocation (assimilation et rapprochement). Dr. Engler is not an unknown worker in phytogeography, for in his various monographs, especially in that of the genus Saxifraga, he has set forth the views which he, in some respectSj more fully elaborates in the work before us. The essay itself is preceded by thirty-six formulated leading ideas (leitende Ideen), which may, for our purpose, be reduced to one, namely, the relation of evolution and geological changes to distribution. Dr. Engler endeavours to trace the descent and migration of the vegetation of the regions under consideration since the Tertiary period by the aid of geological and recent evidence, but for various reasons he does not go back beyond the Miocene period. In his conception of the Miocene period he is in accord with Prof. Heer, who, he thinks, has easily refuted the arguments adduced by Mr. Starkie Gardner in support of his opinion that much of what Prof. Heer regards as Miocene is referable to the Eocene period. The author divides his subject into five sections and eighteen chapters. In the first section he treats of the development of the flora of North America from the Miocene period to the Glacial epoch; the second is devoted to the development of the flora of Eastern and Central Asia since Tertiary times; the third to the main features of the development of the Mediterranean flora since the Tertiary period; the fourth to the development of the high mountain flora before, during, and after the Glacial epoch; and the fifth to the consideration of the development of the floras of other countries influenced by the Glacial period. The map is constructed to show, as nearly as possible, the configuration of land and water in Tertiary times, the direction of the spreading and change of the vegetation during and after the gradual drying-up of the Tertiary seas, and the most important migratory routes of the Glacial plants. Disregarding the evolutionary element, which must necessarily be to a large extent purely speculative, Dr. Engler's essay is exceedingly interesting and instructive. The mere collocation of the facts bearing upon the subject renders it so, independently of the author's deductions therefrom. So far as the migratory part is concerned, it may be designated as an amplification, with some modifications, of the theory recently discussed by Dr. Asa Gray, Sir Joseph Hooker, Mr. Thiselton Dyer, and others. Dr. Engler does not find the contrast so great in the development of the Asiatic element in the vegetation of Eastern and Western North America, and there is no doubt of the existence of many more Asiatic types in Western North America than was formerly suspected. Diligent as the author has been in collecting evidence, he has overlooked some that he would have found useful. Thus at page 29 he seeks to explain the “extraordinarily interrupted distribution” of Monotropa uniflora and Phrymaleptostachya, both of which he assumes to be limited to the Himalayas, North-eastern Asia, and Eastern North America. Now Monotropa uniflora is common in North America west of the Rocky Mountains, as evidenced by specimens and collectors' notes in the Kew Herbarium; and it likewise occurs in Mexico, New Granada, Sachalin, and the Corea. The distribution of Phryma, too, is by no means so restricted as Dr. Engler supposes. But these are minor details which do not affect the main issues. Versuch einer Entwicklungsgeschichte der Pflanzenwelt, insbesondere der Florengebiete sett der Tertiadrperiode. Von Dr. Adolf. Engler. I. Theil. Die Extratropischen Gebiete der Nordlichen Hemisphare. Mit einer chromolithographischen Karte. 8vo. pp. 202. (Leipzig: Verlag von Wilhelm Engelmann, 1879.) Essay of a History of the Evolution of the Vegetable Kingdom, especially of the Floral Areas since the Tertiary Period. Part I.—The Extratropical Regions of the Northern Hemisphere.