June 3, 1920] 



NATURE 



417 



the " hig-h mag-nification crescograph " which mag- 

 nifies the rate of growth up to ten million times. 

 As, even with much lower magnifications, the 

 spot of light or point of the lever would soon 

 move off the scale or recording surface, the 

 author has devised a method of balance different 

 from the optical method originally used. In this 

 new method the plant-holder is connected with a 

 series of gear-wheels driven by a falling- weight 

 and controlled by a fan governor. By this means 

 the plant-holder can be made to fall at various 

 rates, and thus the growth of the plant is com- 

 pensated, and we have what is termed the 

 " balanced crescog-raph. " When the rate of growth 

 is exactly balanced the record will show a hori- 

 zontal line, and any increase or decrease in the 

 rate will be indicated by a rise or fall in the curve. 

 By this means it is claimed that a change in the 

 rate of growth of only i part in 27,000 can be 

 detected. The method is one of great delicacy, 

 if is clear, but, in view of the fact that the control 

 of the speed of movement is in part frictional 

 resistance, and also of the effect of grit and of 

 inequality in the cutting of the gear-wheels, one 

 would have liked to see the inclusion of a record 

 which would demonstrate that a speed of 0-5 m 

 per sec. was kept constant to i part in 25,000 

 for many hours. 



The volume contains thirty chapters on various 

 plant reactions which exhibit themselves either 

 bv movements or by electrical response. Of these 

 perhaps the most striking is the interesting con- 

 tribution which the author makes to the problem 

 of the mechanism of geotropic response. In the 

 statolith theory of geotropism one link in the chain 

 of reactions which bring about geotropic curva- 

 ture is the shifting, under the influence of gravity, 

 of comparatively large starch grains in a tissue 

 such as the endodermis of the stem. This theory is 

 upheld by the author as a result of the explora- 

 tion of the plant by means of his "electric probe." 

 The probe consists of a fine glass tube (01 5 mm, 

 diam.) with a still finer platinum wire fused into, 

 and projecting just beyond, it. The probe can 

 be pushed into the tissues of a stem, while the 

 other end of the platinum wire is connected with 

 one terminal of a galvanometer, the other terminal 

 being connected with some other part of the plant, 

 e.g. a. leaf, which is always kept horizontal. 

 The probe is first placed on the surface of the 

 organ, and the deflection is observed when the 

 stem is placed horizontal; the stem is then re- 

 turned to the vertical position, the probe advanced 

 a little into the tissues, the stem again 

 placed horizontal and the deflection observed. It 

 is found that as the probe penetrates the deflec- 

 NO. 2640, VOL. 105] 



tion rises to a maximum and then falls to a mini- 

 mum at about the centre of the stem. The point 

 of the probe in the position of maximum deflec- 

 tion is found to lie in the endodermis. If the 

 probe is carried forward towards the other side of 

 the stem, a new maximum is found when the point 

 reaches the endodermal layer on the other side, 

 but the deflection is in the opposite direction. 



This observation does not, of course, prove that 

 the endodermis is the geo-perceptive layer, but it 

 provides circumstantial evidence in favour of 

 that view, since it demonstrates that the endo- 

 dermis is the only tissue exhibiting a marked elec- 

 trical reaction to geotropic stimulus. In one 

 case where the angle of the stem was gradually 

 increased there was no deflection until a critical 

 angle of about 33° was reached, but above this 

 there was a marked electrical response. There 

 appears to be some frictional resistance to the 

 displacement of the starch grains, which is not 

 overcome until the critical angle is passed. By 

 comparing the electrical response (which can, of 

 course, be observed without the use of the 

 "probe") of organs placed at angles of 90° and 

 45°, respectively, with the vertical, evidence is 

 obtained in support of the view that the geotropic 

 response is proportional to the sine of the 

 angle. 



The marked effect of temperature on the degree 

 of geotropic response, which leads to decided 

 diurnal movements of many stems, is a thesis 

 which is further elaborated in this volume, as is 

 also the difference between " direct " and " in- 

 direct " stimulation. The volume is filled with 

 numerous and often stimulating observations 

 carried out with the author's well-known mastery 

 of the technique of experimentation. One must 

 be grateful for the new weapons which he has 

 forged and for the new fields of work which he 

 has opened up, but, like Sir J. C. Bose's previous 

 volumes, the present one is often sadly lacking 

 on the plant-physiological side. The work 

 done is never properly related to that of 

 previous investigators, the author confining 

 himself to the quotation of text-books, which 

 are often of no very recent date; in deal- 

 ing with phototropism the work even of Blaauw 

 is not mentioned. Again, Sir J. C. Bose seems 

 so anxious to add to his collection of "plant- 

 records " that he passes rapidly from observation 

 to observation and from problem to problem, 

 shedding on the way a beam of light into some 

 of the dark places of plant physiology, but never 

 satisfying us with a problem fully envisaged and 

 worked out. 



V. H. B. 



