5i8 SCIENCE PROGRESS 



easily. Two chapters are devoted to colloidal solutions and a third to absorption 

 in relation to colloids. A considerable number of references, including practically 

 all the papers from which examples have been taken, are given in footnotes. 



The book possesses an advantage over the majority of elementary books in that 

 no attempt is made to put forward a complex subject in a manner which would 

 suggest to a student that a simple explanation of all the phenomena can be given ; 

 nor does the author insist so strongly on particular theories as is usual. But in 

 expounding a subject in this way, very great care must be exercised. Thus, in 

 dealing with osmosis, after leading up to osmotic pressure from the analogy 

 between diffusion in gases and solutions, the author passes to the conception of 

 osmosis as the result of attraction between solvent and solute in a way which 

 might easily confuse a student unacquainted with the subject. It would perhaps 

 have been advisable to insert a paragraph, such as the second on page 39, at an 

 earlier part of the chapter. 



In the interest of students, protest should be made at the cost of the book ; it 

 is essentially a book for students, not for the library shelf : therefore it should be 

 sold at a price to suit the student's pocket. D. C. 



Fossil Plants. A Textbook for Students of Botany and Geology, Vol. II. By 

 A. C. Seward, M.A., F.R.S. [Pp. xxi + 623, with 265 illustrations.] 

 (Cambridge: University Press, 1910. Price 15^'. net.) 

 During the last few years the shelves of students of Palaeobotany have been 

 enriched by three notable books by British botanists, which are so diverse in 

 their aim and in the method of treatment, though covering much of the same 

 ground, that they will all three be indispensable to serious students of the 

 subject and complementary one of the other. Beside Bower's OHi^in of a Land 

 Flora, and Scott's Studies in Fossil Bo/any, Seward's second volume of Fossil 

 Plants will now take its place, and without doubt will appeal to and be appreciated 

 alike by students of botany and of geology. 



Though twelve years have elapsed since the appearance of the first volume 

 of Fossil Plants, the unavoidable delay which has occurred in publishing the 

 second volume cannot be said to have been of any disadvantage, as it has 

 enabled the author to embody in his later volume many fundamental changes in 

 our conception of the relationship of fossil plants, changes which have been 

 occasioned by the rapid progress of the study of Palaeobotany during the last 

 decade. Luckily comparatively few additions of importance have been made to 

 the subject-matter of vol. i.; on the other hand the advances in our knowledge 

 of the structure of the extinct members of the Lycopodiales, the Filicales, and 

 the Gymnosperms have been so considerable that Prof. Seward has found 

 himself compelled to expand his projected second volume into two volumes, of 

 which the one under review contains an account of the Sphenophyllales, the 

 Lycopodiales and the Filicales, together with some plants of doubtful affinity 

 and some members of the Pteridospernije, that new group of plants the recog- 

 nition of which is due to the careful investigations of Oliver and Scott into the 

 seed-bearing ferns of the Carboniferous period. 



Sphenophyllum, of which the vegetative organs were described in vol. i., 

 is taken up again in vol. ii. ; this commences with an account of the 

 structure of the cone of this plant, of which we know a good deal more by 

 the discovery in 1905 of Sphejiophyllostachys fertilis. Prof. Seward is therefore 

 able to rediscuss the affinities of the Sphenophyllales in the light of the most 

 recent investigations. The interesting fossil, Cheirostrobus, combining some 



