NA TURE 



577 



THURSDAY, APRIL i8, 1895. 



THE EXPERIMENTAL PHYSIOLOGY OF 

 PLANTS. 



Practical Physiology of Plants. By Francis Darwin, 

 M.A., F.R.S., and E. Hamilton Acton, M.A. Cam- 

 bridge Natural Science Manuals, Biological Series. 

 (Cambridge : University Press, 1894.) 



THE physiological course which Mr. Francis Darwin 

 gave at Cambridge in 18S3, was the first sys- 

 tematic effort, in this country, to teach the phenomena 

 of plant-life to students by means of actual experiments. 

 As we are told in the preface to this book, the experi- 

 ments were at first demonstrated in the lecture-room ; 

 some years later, the students were required to do the 

 practical work for themselves in the laboratory. The 

 example set at Cambridge has been followed in other 

 universities and colleges, to the great benefit of botanical 

 teaching. We all recognise now that practical laboratory 

 work is no less necessary in physiological than in mor- 

 phological botany, though in the former it is certainly 

 more difficult to organise. The present book, which 

 embodies the results of the experience gained in prac- 

 tical teaching, is in two parts. Part i., on General 

 Physiology, is the more elementary, and therefore the 

 more widely useful ; Part ii., on the Chemistry of 

 Metabolism, is of a more advanced character, and is 

 adapted to those students who desire to make a special 

 stuJy of the chemical physiology of plants. The former, 

 we believe, is mainly the work of Mr. Darwin ; the 

 latter, of Mr. Acton. ^ 



A volume of this kind was very much needed, and it is 

 a matter for congratulation that the work has fallen into 

 the most competent hands. There was nothing of the 

 kind in English before, and the book will be of the 

 greatest service to both teachers and students. It must 

 be clearly understood that it is a strictly practical la- 

 boratory guide, which can only be used by those who are 

 willing to experiment for themselves. The volume is in 

 no sense a treatise on physiology, and thus differs from its 

 German predecessor, Detmer's " Pflanzen-physiologisches 

 Practicum," which is to some extent a compromise 

 "between a practical guide and a theoretical text-book. 

 The thoroughly practical character of Messrs. Darwin 

 and Acton's book seems to us a great merit ; every word 

 in it is of direct use to the experimental worker, and to 

 him alone. 



We cannot attempt to give anything like a summary 

 of the contents of the work, which, in spite of its 

 moderate bulk, covers a great deal of ground. Thus in 

 part i. alone, no less than 265 distinct experiments are 

 described. Of course they vary very much in character, 

 some being quite simple and elementary, while others 

 are more of the nature of original research. It goes 

 without saying that a large proportion of the experiments 

 are of Mr. Darwin's own devising, and that nearly all 

 have been practically tested by the authors. Wherever 

 this is not the case, the reader is told so ; and if the 

 NO. 1329, VOL. 51] 



experiment is, from any cause, at all likely to fail, he is 

 warned of the possible disappointment. The candour 

 with which the student is treated all through, is a very 

 pleasant feature of the book. 



The first chapter is on some of the conditions affecting 

 t he life of plants, and as the presence of oxygen is 

 among the most important of these conditions, respira- 

 tion is taken first. Besides the more usual experiments, 

 ingenious demonstrations of intramolecular respiration, 

 and of the excessive consumption of oxygen by germinat- 

 ing oily seeds, are given. 



In the second chapter assimilation takes the first place, 

 and many beautiful experiments are described, includ- 

 ing Gardiner's ingenious modification of Sachs's iodine 

 method, in which the sun is made to print off, in starch, 

 a copy of a photograph, from a negative placed on the 

 leaf. An experiment proving that excess of carbon 

 dioxide stops assimilation, is especially interesting. 

 When a second edition is called for, Mr. Blackman's new 

 and important experiments on the function of stomata 

 will no doubt find a place. 



In the next chapter, which is also concerned with nutri- 

 tion, particularly good and complete directions are given 

 for the management of water-cultures ; these are quite 

 the best we have met with, and will save the experimenter 

 from many failures. The use of Duckweed {Lemna) for 

 demonstrating the effect of various food-solutions on 

 growth, is, we believe, new, and is a very neat method. 

 The same chapter includes experiments on the nutrition 

 of the carnivorous plant, Sundew, a subject on which 

 Mr. Darwin's investigations have become classical. 



The question of the movement of water in plants is 

 still unsolved. The data of this problem, however, are 

 very thoroughly taught, by means of the experiments 

 described in the sections on the functions of roots, and on 

 t ranspiration. The latter process is investigated, in the 

 first instance, by means of the potometer, an instrument 

 devised by Mr. Darwin and his pupil Mr. Phillips, in 

 which the speed of the transpiration-current is measured 

 by the rate of ascent of an air-bubble, which is drawn up 

 a capillary glass-tube by a transpiring shoot connected 

 with it. 



A particularly ingenious experiment is one in which 

 the hygroscopic twisting and untwisting of an awn of the 

 g rass Stipa, is made use of as an index of transpiration. 



A chapter on physical and mechanical properties 

 tr eats of such phemonenaas imbibition, turgor, osmosis, 

 a nd the tensions of tissues. It may be pointed out that 

 in the description of Traube's artificial cells, copper 

 i ulphide is evidently a misprint, either for copper chloride, 

 <yc sulphate (p. 1 11). 



The next chapter is on growth, and contains, among 

 ma ny other things, full directions for the use of the 

 various kinds of auxanometer. 



The remaining chapters are concerned with curvatures 

 (geotropism, heliotropism, traumatic | curvature, &c.), 

 and with other movements. Some of the most fascinat- 

 ing experiments come in this part ; we will only mention 

 those on the decapitation of roots, an operation which, 

 as Charles Darwin discovered, prevents the root from per- 

 cei ving the geottopic stimulus, though it does not hinder 



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