Natural auxins 



It is now of interest to compare the course of the rotation curves from the 

 beginning of rotation and onwards, i.e. after they leave the curve for con- 

 tinuous exposure, and this has been done in Figure 7. In the case of exposures 

 for 16 and 32 minutes, the curvature present at the end of the exposure 

 was subtracted from all the later values. The abscissa is the time {T) after 



E-16 to 32 min 



= 0-SSvn\n 



£=0-5m'\r\ 



£L. 



Figure 7. Development of geo tropic 

 curvatures during rotation at i?/0-5 on 

 the klinostat. Ordinate: increase in 

 curvature {C^+ t~'^e) during the period 

 of rotation. Abscissa: time {T) after 

 beginning of rotation. Duration of 

 preceding horizontal exposure (E) 

 indicated for each curve. Data from 

 Figure 6. 



20 



eo 

 Time — •■ 



100 



no 



min 



beginning of rotation. When it comes to exposures of 4 and 0-5 minutes, 

 the graphic transposition requires an assumption as to the course of the 

 lower part of the reaction curve for non-rotated roots. If this curve were to 



Figure 8. Attempt at an estimation 

 of the presentation time. Ordinate: 

 increase in curvature during the rotation 

 (C^+y — C^), readon curves inFigure? 

 at times [T) indicated for each curve. 

 Abscissa: logarithm of the duration 

 of horizontal exposure {E) . The log- 

 arithm of the presentation time {the 

 shortest exposure which will produce a 

 response later) estimated by extra- 

 polation to —0-5, corresponding to a 

 presentation time of 0-3 minutes. 



be extrapolated back as a straight line, a fictitious negative an'gle would be 

 present at the beginning of rotation, and a corresponding angle should be 

 added as a correction. In making this set of curves, however, it was assumed 

 that a positive angle of about 1° was present after 4 minutes of exposure and 

 that practically no curvature was present after 0-5 minutes. 



It is seen that the development of curvatures during the rotation is 

 practically the same after 16 and 32 minutes of exposure. Roots exposed for 

 0-5 and 4 minutes, on the other hand, increase their curvature at a lower rate, 

 and they reach lower maximum values. 



The initial velocity of each of the individual curves probably indicates the 



84 



