( 337 ) 



iinporfaricc. Tims, for instance, we niusl lake si)ec'ial care (hat tlic 

 little cylinder oi- cap does not, by being placed obliqnely, rest with 

 its edge unilaterally against the coleoptile, as may so easily happen; 

 this causes very troul)lesoine contact-curvatures, which might lead 

 to eri-or. We may probably conclude that the reason for Rothkrt's 

 tailure in his experiments on polarity, must be ascribed to these 

 contact-curvatures, which were unknown to him. 



If we now set to work to discover wdiether any basal phototropic 

 curvature effect can be transmitted to the apex then in any case 

 we must first api)ly to the base such a quantity of light that it 

 really curves, in order to be sure that the light has been perceived 

 there. One is at once struck by the fact, that the base is ccrii 

 much less S(')isitire than the ape.r, in spite of the former not being- 

 inferior in rate of growth to the lattei', especially at the higher 

 temperatures at which these experiments were made. I made a 

 determination of sensitiveness as described in the first section and 

 so found that the quantity of light which is necessary to cause 

 a just observable maximal curvature at 25 — 27° C... after Vj^ hours 

 is for the base about 20000 candle meter seconds, whilst that for 

 the apex, at the high temperature employed reaches a value of 

 only 18 candle meter seconds. A very distinct basal curvature was 

 only obtained with 50000 candle meter seconds, a quantity of energy 

 wntli wiiich my first experiments were performed. 



The result of this first series of experiments was to show that 

 after an illumination of the base in this way a phototropic curvature 

 of the apex can never be observed. Now since for a possible apical 

 curvature it might not be indifferent, with wdiat quantity of light 

 the base was illuminated, a large series of experiments were arranged, 

 in which the base was illuminated w^ith very different quantities of 

 light, starting from 'JOO candle meter seconds and gradually mounting 

 to several thousand candle meter seconds. But not in a single one 

 of these cases could curvature of the apex be observed. Tlds is 

 therefore a clear proof of the existence of a pohvitii, of an irrever- 

 sibiiiti/, in the transmission of a phototropic stimulus. 



In order now to trace how far this polarity Avas dependent on 

 the influence of any external conditions, especially having in mind 

 gravitation, we made tw^o new series of experiment's, in \\hi('li 

 first of all suitable coleoptiles wei'e ke|)t in an inverted position 

 during the whole experiment, and in addition experiments in which 

 the coleoptiles were fastened to a clinostat with horizontal axis. 



But in neither of these two series of experiments could any 

 transmission from the base to the a])ex be traced. 



