92 Scientific Intelligence. 



continuous liquid column. In some cases, according to his 

 estimates, this strength exceeds 200 atmospheres. The high pres- 

 sure maintained in the green cells by transpiration is transmitted 

 through this liquid column but is clearly insufficient to rupture 

 it, and in this way the upward passage of the sap is assured. 

 Some of the most interesting of the experiments described by 

 the author are those connected with the determination of the 

 osmotic pressures in cells. They are based on the relationship 

 which exists between the freezing point of a solution and its 

 osmotic pressure, and in the determination of the freezing point 

 an exceedingly delicate thermo-electric method has been employed. 

 Professor Dixon's experiments and conclusions are of much import- 

 ance and throw a great deal of light on one of the most difficult 

 problems in plant physiology. a. w. e. 



2. A Manual of Weeds; with descrijitions of all of the 

 most pernicious and troublesome Plants in the United States and 

 Canada, their habits of growth and distribution, with methods of 

 control ; by Ada E. Georgia. Pp. xi, 593, 386 figs. New York, 



1914 (The Macmillan Company). — The main purpose of the 

 present work is to enable the growers of useful and ornamental 

 plants to recognize and combat the numerous weeds which infest 

 farms and gardens. The introductory chapters deal with general 

 statements about weeds, about the financial loss which they 

 cause, about the ways in which they disseminate themselves, and 

 about the use of chemical herbicides. The body of the book, 

 however, is devoted to full descriptions of individual weeds, and 

 to definite methods of controlling them. The author gives in 

 each case the botanical name of the weed, the English name or 

 names, and tabulated information about the time of blooming, 

 the time of seeding, the geographical distribution, and the hab- 

 itat. The descriptions, although written in semi-popular language, 

 are clear and accurate, and the numerous figures which accom- 

 pany them should help make the determination of the weeds an 

 easy task. The concluding pages give a bibliography, a list of 

 poisonous plants, and a glossary of botanical terms. Miss 

 Georgia's volume is issued in the series of Rural Manuals edited 

 by Professor L. H. Bailey, but it will be found useful not only to 

 those for whom it was written but also to those interested in 

 weeds from a botanical standpoint. A. w. E. 



3. Plant- Breeding ; by L. H. Bailey. New edition revised 

 by Arthur W. Gilbert. Pp. xviii, 474, 113 figs. New York, 



1915 (The Macmillan Company). — As stated in the historical 

 introduction the first edition of Plant-Breeding was published in 

 1895, and the present thoroughly revised edition is the fifth. 

 The topics treated, which will give some idea of the scope of the 

 volume, are the following: variation, mutation, hybridization, 

 heredity, methods of crossing plants, and the forward movement 

 of plant breeding. The discussion of variation and of the 

 important part which it plays in originating new varieties is 

 accompanied by a wealth of illustrative material and is especially 



