36 



of Âvena somewhat more in détail. Rothert') states, 

 that the nutations of Avena do not always hâve a period 

 of the same length ; from his figures on the oscillations 

 in the heliotropic curvation after S'A, 5, 6\4 hour a period 

 of about 180 minutes can be deduced. Rothert mentions 

 further, that more than once he observed the coleoptile 

 completing a rectilinear course of 1 cm. in 60 minutes, 

 which observation quite agrées with my own expérience 

 and points to a period of about 120 minutes. 



The direction of the most vigorous nutation is always 

 the same with regard to the bilaterally symmetrical struc- 

 ture of the coleoptile. The coleoptile indeed is not circular 

 at the top, but elliptical and the main direction of nutation 

 is in the plane of the minor axis of this ellips. As I 

 always planted the germinated oat-grains parallel to each 

 other, I had ample opportunity of comparing nutation in 

 both directions. When gravitation was acting in the 

 direction of the minor axis of the ellips (which at the 

 same time is that of the main axis of the grains), I found the 

 presentation-time shorter ihan in other cases (vide infra, 

 position of plants) ; therefore ail preliminary experiments 

 (séries A and B) were made with plants in this position. 

 Later, after the above-mentioned expériences I always 

 made gravitation act in the direction perpendicular to that 

 of the most vigorous nutation (séries C). 



Taking this information into account we can easily 

 explain thèse reversed curvations as nutations. For this 

 purpose I give the figures of a striking case move fully, 

 quoting from the protocol of my experiment: 



B experiment 75. Date : 18—11—1910. 

 Stimulation-time : 4'40". Temp : 20° C. 

 Not in the thermostat. 



1) W. R o t h e r t, 1894, p. 27—33. 



