202 PHYSIOLOGY [BoT. Absts., Vol. VII, 



1361. KiDD, Franklin, Cyril West, and G. E. Briggs. What is the significance of the 

 efficiency index of plant growth? New Phytol. 19: 88-96. 2 fig. 1920.— This is a critique of 

 the compound interest conception of plant growth advocated by V. H. Blackman and 

 applied by Brenchley in the comparison of the efficiency of different plants. — I. F. Lewis. 



1362. Heinicke, Arthur J. Concerning the shedding of flowers and fruits and other 

 abscission phenomena in apples and pears. Proc. Amer. Soc. Hort. Sci. 16:76-83. 1920. — 

 See Bot. Absts. 7, Entry 977. 



1363. Mitscherlich, E. A. Zum Gesetze des Pfianzenwachstums. [Regarding the law 

 of plant growth.] Flihlings Landw. Zeitg. 68:419-426. 1919. 



MOVEMENTS OF GROWTH AND TURGOR CHANGES 



1364. Guttenberg, Hermann von. Der heutige Stand der Statolithentheorie des 

 Geotropismus. [The present status of the statolith theory of geotropism.] Naturwissenschaf- 

 ten 8: 571-577. 3 fig. 1920. — A review is given of the recent work of Zollikofer, Buder, 

 Richter, and others which add evidence in support of Haberlandt's and Nemec's theory 

 which has called forth so much discussion and experimental work. The arguments of the 

 opponents of this theory (Fitting, Jost, Zielinski, F. & G. Weber, and Heilbronn) are 

 taken up in detail. — Orto7i L. Clark. 



1365. Putter, A. Das Gesetz der Reizschwelle. [The law of the threshold of stimula- 

 tion.] Naturwissenschaften 8: 501-507. 1920.— This paper attempts to show in how far it 

 has been possible to go into a physico-chemical analysis of the threshold of stimulation. 

 This is given in detail for electrical and light stimuli, with a consideration of the formulae 

 of Nernst and Hill for the first, and Putter's own formula for the latter. The difference 

 in the effect of electrical and light stimuli is also pointed out. Light, gravity, and electrical 

 stimuli are grouped as those which may instantly affect the plant at full strength, whereas 

 chemical osmotic, and heat stimuli are effective only after the diffusion of the agents, and a 

 certain time factor is requisite. It is not possible to express in any one formula a general law 

 for the threshold of stimulation, but different equations are required, and these vary with the 

 type of stimuli. In summarizing PtJTTER feels that the necessary conditions of the thresh- 

 old of stimulation may be expressed as "a sensitiveness in a living system when in the system, 

 or at a certain point in it, the concentration of certain active substances reach, in a definite 

 time, a certain magnitude, which is constant for the different systems and different stimuli."— 

 Orton L. Clark. 



1366. Small, James. A theory of geotropism: with some experiments on the chemical re- 

 versal of geotropic response in stem and root. New Phytol. 19: 49-63. 1 pi., 5 fig. 1920.— 

 A statement is made of certain hypotheses previously advanced to explain the difference in 

 electrical condition of the upper and under side of a horizontally placed root, and of geotropic 

 response in general. Curvature is explained on the basis of five postulations. (1) The proto- 

 plasm of the root is characterized by a condition of comparative acidity on the basis of the 

 H-ion concentration as compared with the iso-electric point of the amphoteric colloids present. 



(2) The protein, or protein-lipoid, disperse phase in the root becomes therefore electropositive. 



(3) There is greater polarization on the upper side of any cell and therefore a higher potential 

 in the upper region of the root. (4) An action current flows, therefore, from the upper to the 

 lower side of the perceptive region; on account of the resistance, its maximum effect is pro- 

 duced on the under side of the root. (5) The polarization of the lower cells is thus lowered, 

 their permeability is increased, and the familiar bending phenomena are brought about.— 

 Geotropic response of stems is explained on the same basis, the protoplasm however being 

 electronegative and the flow of the action current being in the reverse direction from that 

 in the root. — Experiments are cited to render greater probability to the theory. Roots of 

 Vicia Faba and maize when grown in an atmosphere containing a low concentration of ammo- 

 nia showed reversal of the usual geotropic response. Conversely, stems became positively 



