146 



NATURE 



[December 19, 1895 



of the seeds of Martynia have been formed, or the 

 delicate tracery of the pappus of Tragopogon, the in- 

 sectivorous glands of Droscra, the roots of Acanihorrhiza 

 which grow upwards and become a thorny hedge around 

 the young plant, or the profusion of thorns upon the 

 palms of moist tropical forests. Although fraught with 

 difficulties, the Darwinian theory embraces all such 

 cases ; while that defended by the author requires a new 

 line of argument in each separate instance. 



Prof. Henslow is rich in expedients, and is a fearless 

 theoriser. He regards the opposite or decussate arrange- 

 ment of leaves as the primitive, because of the position 

 of the cotyledons ; the sheathing base of Monocotyledons 

 and Umbellifers is a mark of degeneracy ; the hetero- 

 phylly oi Juniperusx's, caused by a variation in the amount 

 of nutriment at the plant's disposal. He suggests that 

 the enlarged watery, subterranean parts of desert plants 

 may be due to the blistering action of the hot sand, and 

 that the thickened cuticle of plants in dry climates may 

 be formed or aided by a deoxidation of chlorophyll by 

 excessive light. Lastly, he explains the fact, observed 

 by Volkens, that the stomata of desert plants are fre- 

 quently closed in the day and open at night, by a re- 

 versal of the ordinary reactions of the guard cells to 

 turgescence. " Perhaps the arrested moisture, due to 

 the check to transpiration, may cause turgescence by 

 day, which closes the slit, while its cessation at night 

 brings about a relaxation." 



We confess that Prof Henslow's views on geotropism 

 are puzzling and disappointing. He denies the existence 

 of negative geotropism ; and bases his argument, 

 curiously enough, upon Knight's well-known wheel 

 experiment. Here he discovers a centripetal pulling 

 force which causes the stem apex to grow towards the 

 centre of the rotating wheel, and at the same time a 

 centrifugal pulling force which causes the root to grow 

 outwards. " Each end of the plant is therefore subjected 

 to what might be called an accelerating 'pulling' force." 

 A moment's consideration will show that there is no such 

 centripetal pulling iorce. acting upon the free stem-apex. 

 Prof. Henslow seems to lose sight of the fact that the 

 action of gravity upon parts of plants is directive rather 

 than purely mechanical. 



Further, it is not clear why gravity ceases to act 

 upon the apex of Ranunculus heterophyllus because it is 

 immersed in water (p. 201) ! 



There are many points which will exercise the morpho- 

 logist. Why are the first leaves of water plants regarded 

 as phyllodes ? We hardly agree with Prof. Henslow's 

 ideas on the interchangeability of stems and roots in 

 nature, although each may arise from the other 

 endogenously. 



Then again, it is difficult to follow the author's de- 

 scription of the vascular system of water plants on pages 

 145-7. We gather that he regards "spirals" as the only 

 true " tracheae " ; and " vessels " appear to have quite 

 a different meaning. The following is far from clear : 

 " In aquatics the punctated vessels may closely simulate 

 punctated fibres, the chief differences being in the 

 lessened diameter of the latter, and the more or less 

 oblique pjosition of the septa. Then these pass into 

 thin-walled fibres of the same shape, and finally become 

 ' fibrous cells,' when they may contain starch.'* 

 NO. 1364, VOL. 53] 



We have read the volume with great pleasure, both 

 because pf the mass of interesting details of plant 

 biology, and the ingenious piecing together of evidence ; 

 nevertheless, we do not think that Prof Henslow's 

 attempts to reconstitute the theory of evolution are 

 altogether successful. C. A. Barber. 



SOLUTION AND ELECTROLYSIS. 

 Solution and Electrolysis. By W. C. Dampier Whetham, 

 M.A. (Cambridge: The University Press, 1895.) 



UP till the beginning of the present year the English 

 reader had practically only two text-books to 

 guide him in getting some idea of the scope and import- 

 ance of the Newer Theory of solutions. These were 

 " Solutions," a translation of certain parts of Ostwald's 

 Lehrbuch, and " Outlines of General Chemistry," by the 

 same author. The former gave but an imperfect 

 account of the subject, as it excluded the electrical 

 properties of solutions, and thus the mass of material 

 which groups itself around the hypothesis of electrolytic 

 dissociation ; while the latter, although giving a general 

 survey of the theory, dealt with it in but a superficial 

 manner. To these was added, early in the present year, 

 Nernst's "Theoretical Chemistry," and in this book is to 

 be found the best description in English of the present 

 condition of the theory ; for although the description is 

 by no means rich in records of actual observations, 

 yet, on account of the neat methods used in dealing with 

 the theory of individual questions, and the comprehen- 

 sive mode of attacking the entire subject, it is worthy of 

 the attention of all students of physical chemistry. 



The book under notice gives a much more detailed 

 survey of the theory as a whole than that found in 

 Ostwald's " Outlines." The mode of treatment is, how- 

 ever, less thorough than that in Ostwald's " Solutions,"^ 

 and has little resemblance to the compact and orderly^ 

 method used by Nemst. 



In his preface the author states that a considerable 

 part of the first six chapters is taken from Ostwald's 

 Lehrbuch, and this is unmistakably evident on read- 

 ing them through. They deal with solubility, the different 

 kinds of solutions, diffusion and osmotic pressure, freez- 

 ing-points, and vapour-pressures. The remaining five 

 chapters have much greater claims to originality, and are 

 devoted to the electrical properties of solutions — Fara- 

 day's laws, polarisation, the theory of the voltaic cell, the 

 migration and velocity of the ions, electric conductivity 

 and its correlation with other properties, and theories of 

 electrolysis. 



The student familiar with the elements of physics and' 

 chemistry will have little difficulty in following the in- 

 formation supplied. The author has, in particular, to be 

 thanked for setting out at length the more important 

 applications of thermodynamics to solutions, as these are 

 often a source of worry to the beginner. Many indica- 

 tions are also given of attention to points which are often 

 scantily treated, as in the case of the theory of diffusion,, 

 the meaning of osmotic pressure, the theory of the voltaic 

 cell, &c. On the other hand, the treatment of solutions, 

 in gases, associated solutions, Beckmann's molecular 

 weight apparatus, &c., is extremely superficial. There 



