366 



(\ [\ 



ï\ (\ 



lil l 



10.5 10.20 IC-f-O 10.50 11.5 11.20 11.35 11.50 11.5 IZJZO i.iO 1.25 1 vO 1.55 



Fig. 2 

 Course of the curvature of an Avena saliva seedling. 

 Illuminated from the left with an intensity of 34u G. M. S 

 at 9.30 during 30 sees. Only an apical zone less than 

 1 mm. illuminated. Up to 11.8 a positive curvature, which 

 afterwards passes into a strong negative one. After illu- 

 mination on an intermittent clinostat; temp. 25°. 



If the stiiiiulus is more than 18000 C. M. S., the negative curvat are 

 then decreases again and generally no curvatures at all are observed. 

 The remarkable phenomenon takes place iiowever, that after the 

 very strong stimulus of 400.000 C. M. S. during 4 seconds, weak 

 positive curvatures are seen, which again disap[)ear under the strongest 

 illumination 1 have been able to apply, namely 1.600.000 C.M.S. 



Following these observations of curvatures, which arise after 

 illumination of the apical zone, I am able to give here some results 

 with regard to the sensitiveness of the base. 



Van der Wolk has stated that positive basal curvatures begin to 

 occur at 20000 C. M. S. and are strong at 60000 C. M. S. Von Guttenberg 

 and WiLscHKE have confirmed this. Van der Wolk and von Guttenberg 

 surrounded the apex with little caps of tin-foil. Wilschke thinks 

 this method is wrong and makes use of a very pretty arrangement, 

 by which the light falling through a slit illuminates a definite zone. 



Nevertheless — and Wilschke himself shows this in his paper — 

 this method of using little caps is not as he thinks to be dismissed 

 as wholly useless, because the sensitiveness to contact-stimuli is 

 particularly slight with small caps. Wii.schke's method has the draw- 

 back that only Very little of the material can be used at a time, and 

 this is probably the reason why the phenomena, which will be described 

 here, have escaped his notice. 



I therefore used in my experiments little caps of tin-foil, which 

 were so wide that they could be })laced over the coleoptiles without 

 friction. The little caps were completely light-tight and to make 

 this perfectly sure were surrounded above with sealing-wax : this 

 had at the same time the advantage of making them very easy to 

 handle. They were removed immediately after illumination. 



