December 20, 19 17] 



NATURE 



303 



certain number-problems is discussed ; we g-ather 

 that this application is original on Mr. Dudeney's 

 part. Digital properties are but little known to 

 mathematicians, and we hope his example may 

 serve to direct attention to the method : it was 

 freely used by Bidder, the calculating prodigy, and 

 in a certain class of arithmetical problems is of 

 ;great assistance. 



This notice will indicate generally the lines on 

 which the book is written, and on the whole we 

 should say that it is the best miscellaneous col- 

 lection of the kind with which we are acquainted. 

 The book is profusely illustrated, a marvel of con- 

 densation and cheapness, and singularly free from 

 ambiguities and slips. It would be difficult to 

 find a more attractive present for a schoolboy who 

 is interested (as most schoolboys are) in such 

 problems, for wherever he opens it he will find 

 some amusing puzzle which will tax, and in many 

 ■cases overtax, hus ingenuity. 



FOSSIL BOTANY. 



Fossil Plants : a Text-hook for Students of 

 Botany and Geology. Vol. iii., Pteridospermeae, 

 Cycadofilices, Cordaitales, Cycadophyta. By 

 Prof. A. C. Seward. Pp. xviii + 656. (Cam- 

 bridge : At the University Press, 1917.) Price 

 185, net. 



IN the present instalment of Prof. Seward's 

 well-known text-book on fossil plants the 

 interest of the subject may rightly be said to 

 ^culminate. For this volume deals exclusively 

 with the g^roups of fossil gymnospermous plants, 

 and here between its covers the reader will find 

 spread out for the first time in full and proper 

 perspective the significant discoveries and results 

 of the last fifteen years. The fossil Gymnosperms 

 include the great central groups of seed-plants, 

 and of these one-third of the book is devoted to a 

 consideration of the Pteridosperms and their 

 attendant Cycadofilices, another to the Cycado- 

 ,phyta, whilst the rest is divided between the 

 XDordaiteae and a long chapter on fossil seeds. 

 "This last feature is a most useful digest of a 

 complicated mass of literature, and is a service 

 that will be generally appreciated. 



Modern advance, particularly as to the status 

 jof the Pteridosperms and the Bennettitales 

 (Cycadophyta), has depended primarily on the 

 study of petrifactions derived from Britain, 

 France, and North America, whilst the knowledsfe 

 thus obtained has been reinforced and extended 

 by a critical consideration of impressions from 

 which is gained a sort of twilight picture of these 

 ancient vegetations. Prof. Seward possesses the 

 indispensable qualification in the writer of a book 

 like the present of a practical familiarity in 

 handling both these sources of information — 

 petrifactions and impressions— and when, in addi- 

 tion, the task is performed with such evident 

 sobriety and good judgment, the result Is a book 

 of the greatest permanent value. It should be 

 added that never before has the subject-matter of 

 fossil botany received such full and connected 



NO. 2512, VOL. 100] 



treatment, nor could the marshalling of the facts 

 be bettered. 



In the treatment of his subject-matter the 

 author, in large degree, lets the facts tell their 

 own story. Whilst the theories of fossil botanists 

 are adequately displayed, the author resists all 

 temptations to speculate in the field of plant 

 phylog-eny. Nevertheless, apart from his own rele- 

 vant researches, a g-ood deal of unpublished matter 

 is brought into this book, especially minor points 

 collected from all quarters, each by itself, perhaps, 

 insufficient to justify separate publication, yet in 

 the aggregate appropriately included in a book 

 like this. 



Turning over the pages of this book, it is 

 remarkable how large a share in the establishment 

 of fossil botany has been taken by this country. 

 Following the older period of description under 

 Williamson came a newer epoch of critical re- 

 description, with correlations of members pre- 

 viously scattered. With the momentary exhaus- 

 tion of the English coal-balls of Palaeozoic age, 

 the interest passed to the Bennettitales from the 

 American Jurassic rocks, once more to cross 

 the Atlantic to Scotland, where new forms of 

 great antiquity and interest are now coming- to 

 light. It is to be expected later on that a more 

 intensive and scientific exploitation of our own 

 and the world's coal resources will continue to 

 produce a harvest of fossil plants rich enough 

 to give full occupation to palseobotanlsts, and at 

 the same time still further to elucidate the scheme 

 of evolutlofi of the vegetable kingdom. 



In conclusion It is fitting to mention that this 

 volume is dedicated by Prof. Seward to the 

 memory of the late Proif. C. R. Zeiller, who for 

 so many years was attached to the Ecole des 

 Mines at Paris. Zeiller appealed to workers in 

 this country not only by reason of his lofty charac- 

 ter and eminence as a fossil botanist, but particu- 

 larly because he^ more than any other, established 

 and promoted cordial solidarity between the ranks 

 of fossil botanists on either side of the Channel. It 

 is larg-ely on this account that the recent severe 

 and deplorable losses which the fraternity of 

 palaeobotanists has suffered in France (Including, 

 In addition to Zeiller himself, Ligfnier, Grand'Eury, 

 and the elder Bertrand) have evoked In this country 

 a wide and sympathetic response which only the 

 loss of personal friends can arouse. 



OUR BOOKSHELF. 



With the French Flying Corps. By C. D. 

 WInslow. Pp. 190. (London : Constable and 

 Co., Ltd., 1917.) Price 35. 6d. net. 

 This short volume contains the experiences of an 

 American volunteer who joined the French Flying 

 Service, and gives a brief accoimf of the various 

 steps of his training-. The book can in no sense 

 be called a scientific work ; indeed, the use of 

 technical terms is very loose, as, for instance, the 

 definitions of angle of attack and angle of in- 

 cidence given on p. 30. Statements such as that 

 on p. 26 to the effect that " when two aeroplanes 



