1919] AGRICULTURAL BOTANY. 725 



to the other, and more particularly in tropisms of several sorts which are in- 

 dicated. A study is reported of the relation between response and stimulus 

 of growing and of nongrowing organs. Some of the more important results 

 thus far obtained from experiments are outlined. 



Growth rate under lowering temperature undergoes diminution, and arrest 

 at a dellnite temperature. Temperature rise enhances growth rate to an 

 optimum, after which a decline sets in. At 60° violent contraction occurs, 

 which is termed the spasm of death. The effect of heat is an increase in 

 growth rate, which is retarded by radiation. Very close parallelism has been 

 established betn'een the response given by pulvinated and that by growing 

 organs. Every stimulus gives rise to distinct impulses in two directions, 

 namely, a rapidly propagated hydropositive impulse independent of tissue con- 

 ductivity, and a slowly propagated excitatory negative, dependent upon con- 

 ducting power and considereil as a phenomenon of conduction of protoplasmic 

 change. The former impulse gives rise to expansion, the latter to contraction. 

 Transverse conductivity in the organ is much less than its longitudinal con- 

 ductivity. 



It is claimed that a general statement of the elTect of all kinds of stimuli 

 may be made in the form of the law that direct application of stimulus in- 

 duces contraction and indirect expansion. All induced movements of planrs 

 under environmental changes are, therefore, the definite effects of direct or 

 indirect stimulation. 



A new evaporimeter for use in forest studies, C. G. Bates {U. S. Mo. 

 Weather Rci:, 47 (1919), No. 5, pp. 283-29-'f, pi. 1, figs. //).— This article gives au 

 account of the development and operation of a device, designated as Type 4 

 " sun " wick evaporimeter, which is claimed to give the nearest approach yet 

 attained to complete duplication of the physical features of the plant leaf in 

 relation to the factors which are influential as regards its response to evap- 

 oration stimuli. The Type 4 evaporimeter is said to parallel the total tran- 

 spiration of 12 small coniferous trees more closely than does any other instru- 

 ment yet devised. The instrument is described in detail with enumeration of 

 the advantages claimed for the different features. It is said to be eminently 

 practical, integrating solar and atmospheric conditions in much the same way 

 as does the plant, and no new difficulties presenting when it is used for climato- 

 logical studies continuing throughout the year. 



The temperature coefficient of photosynthesis, W. ,T. V. Osteehout and 

 A. R. C. Haas {Jovr. Gen. Physiol, 1 {1919), No. 3, pp. 295-298) .—T\\e authors 

 have studed photosynthesis in the plant {Ulva rigida) previously noted (E. S. 

 R., 41, p. 523), which forms thin layers permitting adequate control of tempera- 

 ture. This was kept within about 1° of a chosen constant (17 and 27° C.) in 

 sea water containing an indicator and exposed to direct sunlight. Values were 

 obtained from which the authors conclude that the true coefficient of photo- 

 synthesis in that plant within the limits here employed is 1.81. They sug- 

 gest an explanation based upon the assumption that the process involves a 

 light reaction with a low coefficient, followed by an ordinary reaction with a 

 high coefficient. 



Chang'es of electrical conductivity under geotropic stimulation, .1. Small 

 {Proc. Roy. Sac. [London], Scr. B, 90 (191S), No. B, 630, pp. 3-'f9-3(J3, figs. 1^).— 

 The author has made a study of the resistance of the root tip of Yicia faha 

 to the electrical current. The present investigation is claimed to have shown 

 that the mechanism of geotropic response by the roots depends upon changes 

 in permeability, the perception of gravity by plants being thus brought into 

 line with response in animals to the same stimulus. The claim that the 



