1914] CURRENT LITERATURE 89 



the supplement of the angle of deviation from the normal rest position by the 

 11 Schwelle " is a constant. These facts indicate that the organ is most excited by 

 light striking it from directly above, though of course this produces no response. 

 The "Schwelle" for this position is calculated at 6. 7 C.M.S. Some measure- 

 ments were made also on the sporangiophore of Phycomyces and on the mustard 

 seedling. In the latter, as in Avena, the "Schwelle" decreases as the angle of 

 impinging rays passes from the inverse to the normal rest position, while in 

 Phycomyces just the reverse behavior appears. With light striking the organs 

 at right angles, mustard has a " Schwelle" of 240 and Phycomyces 60, against 12 

 C.M.S. for oats. Noack believes he has settled a long-contested point by 

 establishing that the direction of the impinging ray and not the difference in 

 light intensity on two flanks is the determining factor in phototropism. He 

 also takes his results as evidence for the polarization conception of Fitting 

 in conduction of the phototropic stimulus. He believes photoperception and 

 presention are too complex to be explained as simple photochemical reactions, 

 as some have attempted to do. 



Boysen-Jensen 3 repeats and confirms his earlier experiments which 

 showed that the conduction of the phototropic stimulus in the coleoptile of 

 Avena is localized in the half of the seedling not illuminated. He reasserts that 

 Fitting's conception of the polarization in all cells of the organ determined by 

 the direction of the impinging rays is untenable, and finds no evidence for Van 

 der Wolk's claim of wound effects compensating for phototropism. 



Riss,4 working in Jost's laboratory has devised a special sort of centrifuge 

 for the purpose of studying the effect on orthotropic stems and roots of apply- 

 ing centrifugal force equilaterally at right angles to the longitudinal axis of these 

 organs. Such application of centrifugal force, unlike unilaterally applied 

 light, has no tonic effect on the plant organ. This finding is contrary to the 

 assumption of Bach. Such equilaterally applied centrifugal force also causes 

 no modification in the geotropic effect of unilaterally applied gravity, whether 

 the former be applied before, during, or after the latter. In some cases the 

 equilateral force was 20 times the unilateral. This leads to the important 

 conclusion that Weber's law does not apply to geotropic discriminative sensi- 

 bility. Centrifugal force acting in the longitudinal direction inhibits the 

 geotropic effect of a right angle stimulus. The action of gravity at an oblique 

 angle on the orthotropic organ is not a result of the right angle components 

 alone, but the effect of the latter is inhibited by the longitudinal components. 

 For this reason, the author concludes that the sine of angle law of Fitting 

 and Bach does not strictly apply even between 45 and 90 , although the 

 deviation here is slight. The horizontal position of the organ is the position 



3 Boysen-Jensen, P., Uber die Leitung des phototropischen Reizes in der Avena - 

 koleoptile. Ber. Deutsch. Bot. Gesells. 3*:559-5 6 6. 1914. 



4 Riss, Marie-Marthe, tJber den Kinfluss allseitig und in der Langsrirhtung 

 wirkender Schwerkraft auf Wurzeln. Jahrb. Wiss. Bot. 53:157-209. 1913. 



