igo 



NATURE 



{yiUy I, 1880 



regulations as to ceremonial expiation and penance, its 

 tyrannous assertion of Brahminical domination, and its 

 unpractical and unspiritual character will illustrate the 

 condition to which a religion may be brought by mere 

 subtlety and barren meditation, divorced from active life 

 and influenced by an interested priesthood. 



A. H. Sayce 



EVOLUTION OF THE VEGETABLE KINGDOM 

 ] 'ci'such einer Entwicklungsgeschiclite der PJlanzemuelt, 

 insbesondere der FlorcngMcte sett der Teriidrperiode. 

 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. 



13HYTOGEOGRAPHY still presents many difficult 

 problems, the final solution of some of which is ex- 

 tremely 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 Erdc") is a ver)- 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 Ter- 

 tiary 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 assuned determinations are better 

 designated by such terms as affiliation and collocation 

 {assiiiiihition ct rapprochement). Dr. Engler is not an 

 unknown worker in ph>togeography, for in his various 

 monographs, especially in that of the genus Saxifraga, 

 he has set forth the views which he, in some respects, 

 more fully elaborates in the work before us. The essay 

 itself is preceded by thirty-six formulated leading ideas 

 {Icitcnde 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 docs not go back beyond the Miocene period. In his 

 conception of the Miocene period he is in accord with 

 Prof, lleer, who, he thinks, has easily refuted the argu- 

 ments 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 develop- 

 ment 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 moun- 

 tain 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 ele- 

 ment, 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 con- 

 cerned, 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" ol Monotropa 

 uiiiflora 3.ndiPJiryma leptostachya, 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 

 Pliryma, too, is by no means so restricted as Dr. Engler 

 supposes. But these are minor details which do not 

 aftect the main issues. 



Although evolution is the pervading feature of the 

 work, the author nowhere attempts to point out the 

 original types from which other species have descended, 

 as he does in his monograph of the genus Saxifra^a. 

 Bunge, who devoted much time to the study of large 

 genera, constructed a genealogical tree to illustrate the 

 possible descent of the species of Aeantlwlimon, but he 

 admits that the result was eminently unsatisfactory. If 

 so difficult to trace the descent of a genus having the 

 distribution of Acantholimon, we may excuse Dr. Engler 

 for being less successful on the evolution theme than he 

 is on migration. W. B. Hemsley 



LETTERS TO THE EDITOR 



[ The Editor does not hold himself responsible for opinions expressed 

 by his eorrespondaits. Neither can he undertake to return, or 

 to correspond with the writers of, rejected manuscripts. No 

 notiee is taken of anonymous communications. 



[The Editor urgently reqtiests correspondents to keep their letters as 

 short as possible. The pressure on his space is so great that it 

 is impossible otherwise to ensure the appearance even of com- 

 munications containing interesting and novel facts.\ 

 The Freshwater Medusa 

 I OBSERVE in Prof. AUman's article of last week (p. 178) on 



this organism, that he states that the article in question includes 



