162 



TENBKRG Stated liowevei', thai tlie curvature in the third set was 

 smaller than in the other two, and exphiined this discrepancy by 

 assuming a propagalion of the basal curvature to the tip. In m}' 

 opinion it migfit have its cause in the circumstance, that these 

 seedlings were already slightly curved at the moment of the after- 

 illumination, if this had been the ciise, the tip would have received 

 here a smaller quantity of light and this moreover partly under a 

 less favourable angle than in the other sets, and consequently, the 

 phototropic curvature would not have attained the same value. It 

 should also be mentioned, that a repetition of these experiments by 

 Arisz (I.e. p. 105) gave only doubtful results, the souires of ei-ror 

 being very great. In any case, we dare not say, that the acropetal 

 propagation of the basal curvature has been demonstrated, and for 

 the solution of the question, whether an exposition of the basal 

 part exercises any influence on the curvability of the tip, the 

 experiments are not suitable, the intensity of the light being too 

 weak. 



Nevertheless, there are in the paper of Guttfnberg a few indi- 

 cations, which seem to show that the illumination of the basal part 

 influences the curvability of the tip, in the way described by van 

 DKR WoLK. On p. 341 one may read: "Ein deutlicher Unter- 

 schied zwischen den Krinnmungswinkeln der beiden Seriën war dabei 

 nicht zu konstatieren ; doch verhielten sich die allseits vorbeleuchte- 

 ten Pflanzen zunachst etwas anders als die verdunkelten. Bei ersteren 

 erfahrt namlich das oberste Drittel der Koleoptile eine etwas 

 starkere Krümmung als bei letzteren, dafür ist aber bei diesen die 

 Krümmung bereits weiter nach unten fortgeschritten". That these 

 differences were only very small (further data I.e. p. 437) and quan- 

 titatively very different from those observed by van der Wolk, may 

 find its explanation, as I have pointed otit- already, in the feeble 

 intensity of Guttenberg's illumination. 



Arisz mentions (I.e. p. 103), that he has repeated the experiments 

 of VAN DER Wolk, and describes his results in this way: ,,Wohl ist 

 in vielen Fallen eine kleine Vergrösserung der Spitzenkrümmung 

 beobachtet worden, welche auch etwas früher sichtbar wurde, 

 aber so eklatant, wie van der Wolk seine Resultate beschreibt, war 

 es nicht". Arisz therefore does not deny, that the illumination of 

 the basal part enhances the curvability of the tip; only he awards 

 this influence less importance than van der Wolk does. 



Summing up, we may state that our knowledge of the influence 

 which an exposition of the basal part exercises on the tip, is far 

 fron) complete. Moreover, it cannot be said that the available data 



