( 336 ) 



illumine the apex on the anterior side, then we see unequivocally 

 that the base executes a phototropic curvature, although it is some- 

 times necessary to wait longer. This therefore is again proof that 

 BoYSEN Jensen's hypothesis cannot be accepted, but also, that the 

 stimulus can transmit itself past the two wounds which often overlap, 

 that is to say, it does not necessarily take a straight course. 



In short, all these experiments sufficiently show that Boysen 

 Jensen has not interpreted his results correctly. There is no question 

 of localisation of the transmission of phototropic stimulus. The 

 stimulus is transmitted, from the apex to the base, along any 

 arbitrary line, so that the results of Fitting are thus upheld 

 once more. 



§ 3. 



A second problem of the phototropic ti-ansmission of stimulus, 

 with which 1 have occp.pied myself, and shall deal in this section, 

 is the polarity of phototropic stimulus transnussion and some newly 

 discovered facts in conuection with it. 



The polarity of ])hototropic transmission of stimulus was iirst of 

 all discussed by Rothkkt, but as he himself truly says, was iiot 

 demonstrated by him with comj)lete certainty. Since then no one 

 has further concerned himself with it. 



When the coleoptiles of Avena are ilhiuiinated at the apex 

 unilaterally, then the plant executes a phototropic curvature effect 

 towards the base. If we now wish to investigate the polarity of 

 this transmission of stimulus, we have only to illuminate the base 

 in order further to trace to what extent any basal curvature is 

 transmitted towards the apex. It should be clearly understood that 

 henceforth the base and i\[)ex refer to the basal half and the 

 ai)ical half of the coleoptile. Accordingly before I adjusted the 

 necessary little cyliiiders or caps, a very fine line of ink was made 

 at the middle of the coleoptile, which might thus always serve as 

 a guide. In order to be able (o observe clearly the curvature of the 

 apex, I fastened the basal |)art after illuminating it, by means of 

 a closely fitting, unbendable cylinder of tin-foil, made by rolling 

 the foil several times round a little ghiss-tube, of the same, width 

 as the coleoptile. During the illumination of the base the apical 

 portion was always covered \)\ an accurately fitting cap of tin-foil. 

 A really great experimental difficulty arises fiom the sensitiveness 

 of the coleoptile to contact stimulus. We must proceed very 

 carefully, and a knowledge of contact-curvatures as such is of first 



