NATURE 



[March 3, 1910 



constituents of flour, include descriptions of baking- 

 tests, absorption and dough-tests, and the two best- 

 known means of recognising bleached flour, namely, 

 extraction of the colouring matters with light petrol- 

 eum, and the detection of nitrites in the sample. 



An extension which will be found very useful is a 

 separate chapter upon the examination of flavouring- 

 extracts and their substitutes. Processes are given for 

 the determination of vanillin, coumarin, benzaldehyde, 

 lemon oil, wintcrgreen oil, and other essential oils 

 occurring in extracts and essences ; and notes upon 

 adulterants and imitations are also included. 



It will be readily understood that with so large a 

 field to cover a single volume does not, even with a 

 thousand pages, suffice for any exhaustive discussion 

 of the various topics. The really difficult cases of 

 adulteration, the doubtful "border-line" problems, 

 remain always dependent for their solution upon the 

 experience, skill, and wider knowledge possessed by 

 the analyst. Beyond this general observation, how- 

 ever, there is little but praise to bestow upon the book. 

 Apart from one or two misprints, the only questionable 

 matter noticed is the Defren's table on pp. 595-7, 

 where the values of lactose appear rather doubtful ; 

 and one may claim a little grumble at the pounds 

 avoirdupois ; the book is not, in the literal sense, likely 

 to be a vade mecuni. It will lie on the laboratory 

 table, but it will be worth its place there. C. S. 



THE MOVEMENTS OF CHROMATOPHORES 

 IN PLANTS. 

 Die Gestalts- und Lageverdnderung der Pfianzen- 

 Chromatopiioren. By Dr. Gustav Senn. Pp. xv 

 -1-397. (Leipzig : W. Engelmann, 1908.) Price 20 

 marks. 



CHROMATOPHORES in plants were for long re- 

 garded as merely temporarily differentiated 

 fragments of the cytoplasm, and, even within the pre- 

 sent decade, were viewed as cell-organs the physiologi- 

 cal behaviour of which is largely or mainly determined 

 by the general protoplasm ; but more recent investiga- 

 tions have increasingly led botanists to regard chroma- 

 tophores, not only as morphological individuals — so to 

 speak — within the cell, but also as physiological organ- 

 isms in the energid. The climax of this view is the 

 suggestion that chromatophores are in phylogeny 

 nothing more than descendants of parasitic green 

 organisms which entered into symbiosis with cells not 

 possessing chlorophyll. Though this extreme hypo- 

 thesis is not favoured by Dr. Senn, the evidence which 

 he supplies causes him to conclude that chromatophores 

 have larger powers of active contractility and more 

 varied irritability than has hitherto been believed. He 

 concludes that their change of shape and movements 

 in the cell are exclusively or mainly the result of 

 their own special activity, and that they are not 

 passively distorted or transported by the cytoplasm 

 '(though he naturally admits their passive carriage 

 •by rotating protoplasm and the like)! 



The book begins with the consideration of the 

 change of shape of the individual chloroplast, a phen- 

 omenon generally neglected by botanical teachers, 

 though easily visible in such familiar laboratory types 

 NO. 2105, VOL. 83] 



as Funaria and Vaucheria. Dr. Senn describes the 

 changes of shape in a number of types, and discusses 

 the parts played in causing them by light, temperature, 

 and chemical and other agencies. His general con- 

 clusion is that change of shape of the chromatophore 

 is occasioned by "diffuse," not directive stimuli. 



The main mass of the book deals, however, with 

 changes in position of the chromatophores in the cell. 

 Eight different patterns of distribution are recognised 

 — epistrophe, apostrophe, systrophe (round the 

 nucleus), peristrophe (uniformly round the cell-walls), 

 antistrophe (on the wall facing the light), diastrophe 

 (on the wall facing the light and on that opposed to it), 

 parastrophe (in shaded parts of the cell), and escharo- 

 strophe (at the focus of the rays of light entering the 

 cell). The conclusion is drawn that change of position 

 of the chromatophores in the cell is the result of 

 "tropic tactic [taxis] stimulus," in which the 

 direction of the stimulus (for instance, light) does not 

 as such determine the result, but only does so in- 

 directly by involving a difference in intensity. Accord- 

 ing to Dr. Senn the distribution of the chromatophores 

 in the cell is not the result of a simple stimulus 

 emanating from the general protoplasm or released 

 by differences in turgidity, but is the consequence of 

 several types of irritability (phototaxis, chemotaxis, 

 thermotaxis, osmotaxis) possessed by the chromato- 

 phores, which thus react in the same manner as free 

 zoospores or Protozoa. 



An appendix treats of the refractive index of the 

 plant cell. 



In a brief notice it is impossible to do justice to the 

 wealth of detail in the book, which, except in the 

 case of the special investigator, is one to be consulted 

 rather than read through ; indeed, the present reviewej 

 confesses that he has not read the whole of the 376 

 pages of text. 



Apart from containing the results of prolonged re- 

 search and numerous observations, this critical book 

 derives value from the thorough manner in which 

 the author considers and does justice to the work of 

 his predecessors, also from the repeated summaries of 

 the conclusions arrived at concerning the various 

 problems investigated, and from the rich bibliography 

 and excellent index. The book, in fact, is one that 

 should at least be in the library of every botanical 

 institute. 



MODERN ALGEBRA. 



(i) A New Algebra. By S. Barnard and J. M. Child. 



Parts i.-iv., wuth answers. Pp. X4-534. Price 45. 



Part iv., with answers. Pp. x + (301-466). Price 



IS. gd. (London : Macmillan and Co., Ltd., 1909.) 



(2) College Algebra. By Dr. S. C. Davisson. Pp. 



ix+ 191. (New York : The Macmillan Co. ; London : 



Macmillan and Co., Ltd., 1909.) Price 7s. 6d. 



(i)Tn*EW branches of elementary mathematics have 



J- escaped the hand of the reformer during the 



last ten years. That this is a healthy symptom is 



unquestionable, for at least it points to a revival of 



interest, which cannot but infuse fresh life into a 



subject that the monotony of time may render arid 



and perfunctory. What measure of favour is to be 



