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SCIENCE 



[N. S. Vol. XXVIII. No. 723 



whicli lie writes, and his book reveals an inti- 

 mate and professional knowledge of his sub- 

 ject. It is not, however, addressed exclusively 

 to a professional audience; while not exactly 

 food for babes, it does not assume an exten- 

 sive preliminary knowledge of the subject, 

 and the necessary mathematical developments 

 are presented in an elementary way, so that 

 any one who is not averse to recalling his 

 knowledge of elementary algebra and geom- 

 etry may read the book with pleasure and 

 profit. 



A marked characteristic of modern physics 

 is the free and fearless use of hypotheses — a 

 use which would have been regarded as 

 dangerous, or at least unscrupulous, in the 

 days before we had been taught by the 

 example of great masters like Faraday, Kelvin 

 and Maxwell, that hypotheses were the most 

 useful of all the instruments of research. In 

 those days a hypothesis was considered to be 

 justifiable only when its author could look for- 

 ward with confidence to the time when it 

 should be raised to the greater dignity of a 

 "theory," and perhaps ultimately be proved 

 to be " true." How far we have advanced 

 from this position is indicated by Professor 

 J. J. Thomson's remark that a physical theory 

 is not a creed, but a policy, and by Mr. Camp- 

 bell's statement (p. 231) that "a false hypo- 

 thesis is better than none." This attitude 

 must, of course, be thoroughly understood by 

 the reader. He must recognize that the 

 model structures which are used in this book 

 to explain electrical and optical phenomena 

 are not the only ones possible even at the 

 present time; and that, as investigation pro- 

 ceeds, they will have to be modified and in 

 many cases rejected altogether in favor of 

 others which more perfectly represent the re- 

 sults of experience. 



H. A. BUMSTEAD 



Einleitung in die Experimenielle Morphologie 

 der Pflanzen. Von Dr. K. Goebel. 8vo, 

 pp. vi + 260, with 135 figures. Leipzig and 

 Berlin, B. G. Teubner. 1908. Price 8 

 Marks. 

 This book, which is an amplification of a 



series of lectures delivered by Professor 



Goebel in the winter of 1906-Y, is one of the 

 most suggestive botanical contributions of re- 

 cent years. Not only botanists of moderate 

 training, but scientific gardeners should be 

 able to read the work, repeat the experiments 

 and devise new ones. The apparatus is 

 usually very simple, as the author says, " a 

 plant, a pot of dirt and a question." Little 

 attention is paid to the direct effect of light, 

 heat, etc., the reader being directed to Pfeffer's 

 " Pflanzenphysiologie," and Goebel's " Organ- 

 ographie " for a discussion of these factors. 

 For experimental work on lower plants, refer- 

 ence is made to Klebs's " Ueber Probleme der 

 Entwickelung." 



There is no attempt at completeness, the 

 book being intentionally an introduction 

 rather than a hand-book. 



The titles of the five chapters indicate the 

 scope of the work. (1) The Field of Experi- 

 mental Morphology, (2) Influencing the Form 

 of the Leaf by Internal and External Condi- 

 tions, (3) Conditions for the Various Develop- 

 ment of Main and Side Axes, (4) Eegenera- 

 tion, (5) Polarity. 



In addition to the question, How does de- 

 velopment proceed, there is another, why does 

 it so proceed. The book is most deeply con- 

 cerned with the second question. Plants 

 diverging from the usual form are called 

 freaks; some plants develop one form under 

 moist conditions and another under dry ; some 

 plants have juvenile stages quite different 

 from the adult form; injuries often cause a 

 plant to develop in a direction not followed 

 by the normal plant, etc. Experimental 

 morphology attempts to answer the questions 

 raised by such phenomena. That heredity 

 must be reckoned with is not questioned. The 

 acorn gives rise to an oak, and the beech nut 

 to a beech tree; but normal stages in develop- 

 ment may be skipped, after a later stage there 

 may be a return to an earlier, and this because 

 the various stages in development are de- 

 pendent upon internal conditions which may 

 be influenced by external factors. Develop- 

 ment may be checked at a certain stage, when 

 conditions for the succeeding stage are not 

 present. 



