February 3, 1921] 



NATURE 



723 



An appendix contains useful references for further 

 reading. 



By a strang-e oversight, chap. v. begins with 

 types of equations "solvable for p" where not 

 only has p not been defined, but the letter has 

 also been repeatedly used on previous pages in dif- 

 ferent senses. Of course, the third line in ex. i. 

 of paras. 52 and 53 will reveal the new signifi- 

 cation to a smart reader, though the private 

 student, as a rule, will be completely at sea for 

 a time. There are other minor points, which will, 

 no doubt, be attended to in the second edition ; 

 but space forbids us to say more than that, in this 

 most interesting volume, Prof. Piaggio has proved 

 himself to be a teacher of remarkable insight and 

 skill. 



(2) We know of no better introduction to the 

 elements of algebra than that by Mr. Durell, of 

 Winchester, and the late Mr. Palmer, of Christ's 

 Hospital. The authors have contrived a course 

 in which there is scarcely a page without ample 

 evidence of intimate care controlled by a profound 

 knowledge of youthful psychology. To many, the 

 greatest attraction in the book is the fact that so 

 large a proportion of it is adapted for viva voce 

 work, and in accordance with modern ideas the 

 material is throughout selected so as to bring the 

 pupil as soon as fKjssible within sight of the 

 applications of the subject to the affairs of every- 

 day life, and to such elementary scientific work 

 as may be fairly expected to have come within 

 his experience. The usual explanatory matter, 

 which few boys and girls ever read, is reduced to 

 a minimum, and placed in an "introduction" of 

 about twenty pages. Useful extensions of various 

 sections for the benefit of the few irrepressibles 

 who cannot be kept back, and for the budding 

 engineers and future specialists, are added in a 

 final chapter. The writer of this notice can speak 

 with personal experience of the successful manner 

 in which a training on these lines copes with the in- 

 ertia which lies at the base of most, if not, indeed, 

 of all, of the difficulties that confront the beginner. 

 In the hands of a sound teacher the pupil's rate 

 of progress will be as rapid as he chooses, and 

 the book may be placed with confidence in the 

 hands of the private student. The collection of 

 sixty odd pages of well-graded revision papers of 

 various stages of difficulty adds considerably to 

 the general value of the book. 



(3) The short course of college mathematics 

 by Prof. Moritz, professor of mathematics in 

 Washington University, was originally devised to 

 meet the demand during the war for short courses. 

 So far as it goes, the treatment is thorough ; the 

 sixty pages on graphic methods are well and 



NO. 2675, VOL. 106] 



plentifully illustrated, and the student who has 

 mastered the book should have a sound grasp 

 of the essentials of trigonometry. 



(4) The second part of Messrs. Dobbs and 

 Marsden's "Arithmetic" consists of collections of 

 papers, with the minimum of explanatory text, 

 covering easy mensuration, financial subjects, 

 graphs, and applications of elementary arith- 

 metical notions to such problems as specific 

 gravity, map-reading, etc. About half the book 

 is given to revision papers. There is considerable 

 variety in the carefully selected sets of questions. 



Our Bookshelf. 



Heredity and Evolution in Plants. By C. Stuart 

 Gager. Pp. xv + 265. (Philadelphia : P. Blaki- 

 ston's Son and Co., 1920.) 



This little book is an expansion of several chapters 

 of the author's "Fundamentals of Botany." It is 

 intended for beginners and general readers, and 

 presents in a fresh way a very readable and well- 

 illustrated account of the phenomena of heredity 

 and evolution from the strictly botanical point of 

 view. The author begins quite unexpectedly with 

 two chapters on the life-history of a fern, and this 

 concise account, followed by a chapter on funda- 

 mental principles, forms a background for the 

 treatment of the subject proper. The definition 

 of heredity as "the genetic relationship that exists 

 between successive generations of organisms " 

 omits to recognise the fact that the conception of 

 heredity is fundamentally concerned with resem- 

 blances and differences as they occur in genetically 

 related organisms. Later chapters deal with 

 Mendelism, evolution, Darwinism, and experi- 

 mental evolution. A very good balance is pre- 

 served between the historical and the descriptive 

 methods, with a sprinkling of illustrations, the 

 majority of which are new to text-books. 



A chapter on the evolution of plants touches 

 upon such problems as alternation of generations, 

 evolution of the sporophyte, and the evidence from 

 comparative anatomy, and ends with a hypo- 

 thetical ancestral tree of relationships. One of 

 the subjects best treated is that of geo- 

 graphical distribution, which discusses the means 

 of dispersal, peculiarities of distribution, effects of 

 glaciation and cultivation on distribution, en- 

 dcmism, the "age and area " hypothesis of Willis, 

 etc., with numerous illustrative cases from the 

 recent literature. The final chapters deal with the 

 fossil record and the various hypothetical relation- 

 ships of the groups of vascular plants. 



The book is well produced and relatively free 

 from typographical errors. We notice a slip 

 (p. 42) in the statement regarding the multiplica- 

 tion of the offspring from a mustard plant. Many 

 general readers will find enjoyment and informa- 

 tion in a pcru.sal of this little book. 



R. R. c;. 



