( 331 ) 



we seek tbr the (|ii;iiilil_v of eiiorjiv wliicli is ;ii;aiii iieccssjirv in order 

 lo g'ive a niaxiinal ('iir\;i(ure, aftei' half an lioni'. These Iwo maximal 

 eurvatures will then i)e of the same magnitiule, Imi th^ ([nanlily of 

 energy necessary, will be less in the ease of the more sensitive plant. 

 Further, whenever the sensitiveness is mentioned, the temperature 

 should always be given, as this is of vei-y great influence on the 

 sensitiveness. 



Observation of the maximal curvature taives place by means of a 

 glass plate provided with a millimetre scale on which an image of 

 the coleoptile is projected by means of a lens. Nevertheless, with 

 some experience it is possible to observe with the naked eye the 

 maximal curvature by repeatedly looking at and comparing the 

 experimental objects. Of course red light is always used. 



It so happens that Blaauw and FR<)ScnF,T, have always worked 

 with the quantity of energy, which is necessary to produce a maximal 

 curvature after i^'.^ — 2 hours, just visible to the naked eye. But as 

 they did not pay special attention to the maximum of curvature, 

 the values they obtained for the quantity of energy are somewhat 

 divergent. 



Finally, it must be specially remembered that the coleoptiles 

 execute, their strongest nutation in the median plane, i.e. the i)lane 

 passing through the longitudinal axis of the grain ^), so that slinui- 

 latiou should always lake place in a direction i)erpcndicular to this, 

 in the transverse plane therefore. 



§ 2. 



It is fairly intelligible that, now when the physiology of stimulation 

 has developed more and more in every direction, renewed interest is 

 taken in investigating the problem of transmission of stimulus, at 

 the same time with some hope that from this side also a step might 

 be taken towards the solution of the problem of stimulus, a problem 

 obviously beset with great difficulties. 



Various investigators have already had the study of the trans- 

 mission of stimuli in plants on their programme of work, but for 

 all that it has remained in many aspects an obscure question and 

 unfortunately the points at issue have quite recently again increased 

 in number. 



Thus in this section I wish to criticise the recent investigation of 

 BoYSEN JïiNSEN ^j, whicli, by its remarkable and somewhat unexpected 



^) A. A. L. Rutgers. Do invloed der temperaliuir op den praescnlalietijd l)ij 

 geotropie. (Diss. Ulrechl 1910 ) 



-) P. BoYSEN Jensen. La transmission de rirritation phototropiquc dans I'Avena. 

 (Acad. roy. d. Sc. et des lelt. de Danemark, 1911. N". 1. 



23 



Proceedings Royal Acad. Arasterdam. Vol. XIV. 



