368 



by illumination of the apex and of the base, it is found that in 

 order to obtain a positive curvature of the apex a smaller amount 

 of light is sufficient than for one of the base. The negative influence 

 in the base and especially in the most basal zones is however visible 

 with smaller amounts of light. 



It is most remarkable that also the negative geotropic curvature, 

 which JosT and R. Stoppel ^) found at high centrifugal forces were 

 strongest in the more basal zones. Whether this is due to the greater 

 rate of growth in the basal zones in comparison with the apex can 

 only be decided by future investigations. 



The results described point to (he possibility of explaining the 

 aberrant results obtained by von Guttenberg and van dek Wolk. 

 Van der Wolk held that illumination of the base makes the apex 

 more sensitive to an illumination from the opposite side, whilst 

 VON Guttenberg observed a smaller reaction of the apex. I also 

 have been able to confirm von Guttenberg's result. He applied 40000 

 C. M. S. in one hour, obtained therefore a strong positive basal 

 curvature and then concludes from the decreased apical curvature 

 that there is a conduction of stimulus towards the apex. Unfor- 

 tunately it is impossible to repeat the experiments of van der Wolk, 

 because he did not state what quantity of energy he used for illu- 

 mination and in what time this was applied. If however this was 

 in a short time, (hen the assumption is obvious, that he was dealing 

 with a zone in which negative curvatures arose, which superimposed 

 on an apical curvature caused by illumination of the apex from the 

 other side, produced a stronger effect in this direction, thus giving 

 rise to the impression that the apex through the previous illumination 

 of the base had become more sensitive. Experiments carried out in 

 this direction have not led to a conclusive result, although a basal 

 illumination of the base with 20000 C. M. S. and an apical illumination 

 from the opposite side with 15 C M. S. indeed produce apical curva- 

 ture sooner and often rather more strongly than in plants without 

 basal illumination ^\ I have not obtained such striking results as 

 those described by van der Wolk, although the possibility is by no 

 means excluded that taking a somewhat different length of the 

 illuminated part and some other amount of energy, applied perhaps 

 during a longer time, the phenomenon may show itself more markedly. 



Utrecht, Botanical Laboratory. 



1) Zeitschr. f. Bot. Bd. 4 1913. 



~) It 120000 G. M. S. in 60 sec. is applied to the base then the apical curvature 

 is uoliceably slighter, because in this case a positive basal curvature predominates. 



