REVIEWS ' 501 



found in cargoes, ballast, and impure seeds ; and that new-comers, so 

 imported, often get a strong hold on their new terrain. A chapter on the 

 methods of preventing and eradicating weeds follows, and the vitality of 

 weed seeds is then discussed. Preventive measures were foreshadowed 

 already in the consideration of the methods of spreading ; while under 

 curative measures both mechanical means — special methods of cultivation — 

 and chemical means — treatment with sprays and manures — are critically 

 examined. The practical importance of the length of life of seeds, if not so 

 obvious, is none the less real ; as buried seeds remain alive for considerable 

 periods, in the case of the gorse seeds, here mentioned, for at least twenty-five 

 years. The problem raises wider issues, and we would have wished to 

 be presented with a fuller account of the causes which have been suggested 

 as active in inducing dormancy. It is interesting to learn that the author's 

 own work has substantiated the view, widely held by farmers, that charlock 

 seeds, when buried, are long-lived ; and as interesting to note that the 

 opinion that creeping thistle seeds are abortive is contrary to the facts. 



Dr. Brenchley, in considering the association of weeds with soils, largely 

 makes use of her own work on this part of the subject. She finds herself at 

 variance, on several points, with the other workers who do not seem to have 

 dealt with such a variety of districts nor to have treated their results in a 

 quantitative manner. More confidence could be placed in the results here 

 put forward if they were accompanied by analyses, mechanical and chemical, 

 of the soils whose weed floras were investigated. The uses and habits of 

 weeds are treated of, and poisonous, injurious, and parasitic weeds are 

 described, with special methods of eradication. There is only a quite inci- 

 dental mention of the damage that weeds may cause through being the 

 bearers of diseases that can also attack crops. 



There are a number of illustrations to the volume — we do not seem to 

 be told anywhere who is responsible for them — and many of them, especially 

 some of the habit-drawings, deserve a special word of praise. 



E. M. C. 



ZOOLOGY 



Principles of Animal. Biology. By A. F. Shull, with the collaboration of 

 G. R. Larue and A. G. Ruthven. [Pp 441 + xv, with a frontispiece 

 and 244 illustrations.] New York and London : The Graw-Hill Book 

 Co., 1920. Price 21s. net.) 



Some years ago the University of Michigan replaced its introductory course 

 in Zoology based upon the type system by one treating mainly of principles, 

 and the present volume is a textbook suited for such a course. It was thought, 

 however, that even in laboratories where the type system is stiU adopted it 

 would be useful to have such a book to supplement the morphological work. 

 While it is questionable whether it is wise to entirely replace a morphological 

 course by one dealing with principles, there can be no doubt that some such 

 work as the present could be read with advantage in correlation with any 

 introductory course in Zoology. 



Most of the information in it is available in textbooks and other volumes 

 to be found in any Zoological laboratory, but it is here sifted and collected in 

 relation to the various subjects dealt with in the sixteen chapters. Thereby 

 the junior student is saved a considerable amount of time. 



One of the features of the book is a fairly extensive glossary which is very 

 useful to a beginner, but we cannot help thinking that even in an elementary 

 work some of the definitions could be more concise and that its value would 

 be greatly enhanced by giving the derivations of most of the terms used. 



The book is readably written and well illustrated. 



C. H. O'D. 



