( 830 ) 



had been previously- illuniiiuiled, the amotiut was only about 12 

 candle meter seconds. Throwjli lllamination of tJic base th<' ape.i- 

 there/ore became more sensitive. 



This fact is very remarkable; for let us at once lay emphasis on 

 the fact that the adequacy of a small amount of light necessary to 

 make the apex curve, when the base is illuminated, is not at all a 

 question of summation; for an effective sununation only occurs in 

 unilateral stimulation, whilst in the present case the increase of 

 sensitiveness is on every side; summation does not therefore come 

 into consideration. 



This diifuse enrichment with light energy might to some extent be 

 compared with an all-round direct illumination of the apex, but, and 

 here I lüish to lay special emphasis, we know from phototropic 

 attnnement, that on the contrary an all-round illumination diminishes 

 the sensitiveness; the conception of sensitiveness in the present incesti- 

 gation is therefore completeh/ opposed to the notion of attiuiin<i and 

 maij in no way be identified ivith it. 



What has been established with regard to the influence of tlie 

 illuminated base on the apex was also found to be true of the 

 influence of the illuminated apex on the darkened base. 



Since in the latter case we have the difficulty of the phototropic 

 curvature effect being transmitted to the base, the top half of the 

 coleoptile w^as cut off, three minutes after the illumination of the 

 base. Three minutes, and most probably even less, were sufficient 

 foi' the base to show already the influence of the illuminated apex, 

 again in the sense that the base becomes more sensitive. Control 

 experiments prove that by means of the current of sensitiveness 

 alone, hence without the direct illumination following upon it, a 

 curvature of the base never occurred. All that we know of the trans- 

 mission of the curvature effect from the apex makes it improbable, 

 tliat in tiie three minutes (a time which in all probability might be 

 further diminished), the cui-xature effect would have already reached 

 the base. We can confidently say that there is also here, as in the 

 case of increased apical sensitiveness, a current of sensitiveness which 

 as it were travels like a shock through the plant at the moment of 

 illumination. 



§ 4. 



As a result of the experimoiUs described above, we can say that 

 it is here very clearly found that perception and reaction are two 

 wholly different processes. We have seen how on illiunination a 

 current of sensitiveness travels almost immediately through the 



