Feb. 17, 1 88 1 J 



NA TURE 



359 



ably be a vera causa in the production of terrestrial 

 climate, and must always tend to produce alternate mild 

 and severe conditions, there must be some counteracting 

 cause whereby these influences are weakened or neu- 

 tralised. This modifying effect he assigns to changes 

 in the distribution of land and sea, especially in high 

 latitudes. He contends that without lofty land there 

 can be no permanent snow and ice. Consequently by the 

 due elevation of Arctic land an area would be provided on 

 which, when winter occurred in aphelion during a period 

 of high excentricity, there would be so copious an accu- 

 mulation of snow and ice, that even during perihelion 

 the wintry conditions would continue, and perhaps even 

 in an intensified form. Subsidence of this land, however 

 would admit the warm oceanic currents from lower lati- 

 tudes, and so great would be the amount of heat thereby 

 transferred that even winter occurring when the North , 

 Pole was turned from the sun and the earth's orbit was at ! 

 a maximum of excentricity would be insufficient to cover 

 the Polar regions with an ice-cap. The alternate phases 

 of precession, which tend to bring warmer and colder \ 

 conditions of climate every 10,500 years, would introduce ! 

 a complete climatal change only where the land was 

 partially snow-clad. The general conclusion is thus ' 

 reached that, the climates of the globe being mainly ' 

 dependent on geographical conditions, their mutations in 

 former periods have been chiefly brought about by changes 

 in physical geography. Mr. Wallace supports these views 

 by much ingenious reasoning. He argues that during by 

 far the greater part of geological time the distribution of 

 land has been such that warm oceanic currents have been 

 able to pass freely to the North Pole, giving a mild 

 climate to the whole northern hemisphere. He would 

 thus account for the palaontological evidence of long- 

 continued glacial conditions within the Arctic circle from 

 Palajozoic to late Tertiary times. It was only in very 

 recent times, he thinks, that the great northern continents 

 became so completely consolidated as to shut out the 

 tropical currents and to render possible the wide-spread 

 and intense glaciation which was actually brought about 

 by the high excentricity that occurred about 200,000 years 

 ago. According to this view geographical revolutions 

 "have been the chief, if not the exclusive, causes of the 

 long-continued mild climates of the Arctic regions, while 

 the concurrence of astronomical influences has been 

 essential to the production of glacial epochs in the 

 temperate zones, as well as of local glaciations in low 

 latitudes." 



In a remarkable chapter, remarkable as the deliberate 

 judgment of an accomplished naturalist, the author 

 decides that the vast periods of time which used to be 

 demanded for the changes of geological history are not 

 required even for the evolution of the floras and faunas 

 of the earth. He admits, with some geologists who have 

 advanced the same view from physical data, that geolo- 

 gical changes probably occurred more vigorously and 

 rapidly in former times than they do at present, and as 

 these changes have always been accompanied by relative 

 alterations in the forms of the organic world, he believes 

 that organic evolution has taken place far more rapidly 

 than has been hitherto thought possible. 



Arch. Geikie 



ALG/E 

 Species, Genera, et Ordines Algarum, seu descriptiones sue- 



dncta specieriim, generum,et ordinum, guibus Algarmn 



regnum constituitur, auctore Jarobo Georgia Agardh, 



Bot. in Acad. Ljind. Prof. Enter. Vol. iii. pars ii. 



8vo. pp. 3ot. (Lipsia; : apud T. O. Weigel, 1880.) 

 'T'HE appeirance of Dr. J. G. Agardh's excellent work, 

 ^ " Florideernes Morphologi," published in the Ada 

 of the Royal Scientific Academy of Stockholm, was duly 

 noticed in the pages of Nature (vol. xxi. p. 282), but, as 

 the work was written in Swedish, a knowledge of its 

 contents was accessible to a limited number of students 

 only ; the indefatigable author has therefore, with a view 

 to render it more useful to those who take an interest in 

 his subject, now issued an edition in Latin of the 

 Morphology. 



This new volume, which is in 8vo, forms the second 

 part of the third volume of Dr. Agardh's " Species, 

 Genera, et Ordines Algarum," and may be considered 

 rather as a revised edition of the Swedish work than as 

 an exact translation of it. The author has made some 

 alterations both in the text and in the notes. These 

 alterations include important remarks on the most recent 

 algological publications, including M. Bornet's " Notes 

 Algologiques," M. Sirodot's observations on the fecunda- 

 tion of the Batrachospermeae, and those of M. Dodel-Port 

 on the fertilisation of the spores of Alga; by Vorticellae. 



For a summary of the contents of the new work the 

 reader is referred to the before-mentioned notice in 

 Nature ; it may however be remarked that the present 

 volume forms a valuable addition to the " Species, Genera, 

 et Ordines Algarum," to which it is now appended, and 

 its appearance will undoubtedly be welcomed by all who 

 take an interest in the morphology of Algffi. 



In addition to a table of contents and an index rerum, 

 there is also an index of the species referred to. The 

 latter is the more useful, because, in addition to the name 

 of the species, there are special references to the descrip- 

 tions of the structure, ramification, reproductive organs, 

 and other particulars relating to the plants. This arrange- 

 ment is especially convenient, inasmuch as these matters 

 are treated separately in different parts of the work. 



It is to be regretted that the beautiful illustrations 

 appended to the Swedish edition do not accompany the 

 present. The figures are referred to in the latter, and 

 may be consulted by those who are fortunate enough to 

 possess a copy of the former, or who have access to 

 libraries which contain copies of the Acta of the before- 

 mentioned Swedish Academy. It may be added that 

 Dr. Agardh's descriptions of the parts of the plants are 

 expressed with his usual precision and clearness, and can, 

 therefore, be understood without the plates— though, 

 undoubtedly, better with them. 



It may be observed that the present volume treats 

 solely of the morphology of the Floridere, and the author 

 does not allude to the classification of Algae, except to 

 express his opinion that certain Algae of red or purple 

 colours, such as Bangic-c and Porphyrse, included by 

 many algologists among the Florides, do not really 

 belong to that class (p. 9, note). MM. Thuret and Le 

 Jolis excluded these plants from the old class of chloro- 

 sperms, to which they were formerly considered to belong. 



