Botany. — "On stimulation in au.rotonic movements" . By Prof. 

 J. M. Janse. (Communicated by Prof. J. C. Schoute). 



(Communicated at the Meeting of January 27, 1923). 



Many movements (curvatures) of very different plant-organs are 

 caused hy a change in the speed of growth on one side of the 

 organ; collectively they are often called "auxotoiiic" movements. 

 Various stimuli, among which those of gravilalion and of light are 

 by far the most important, may be the indirect cause of these 

 movements; these stimuli are received locally and conducted to tiie 

 growing zone in which the bending will afterwards take place. 



The theory iutherto generally accepted was that the normal 

 vertical longitudinal growth was a separate phenomenon, and that, 

 for instance, the gravitation-stimulus appeared only after the plant- 

 organ had been given a different position. In a recently published 

 paper '), I expressed as my opinion that, on the contrary, the 

 normal length-growth is also due to the gravitation-stimulus whicii 

 by an increased growth of the cells equally on all sides would 

 cause, for instance, the vertical growth of the main-a.\is and of the 

 radicle. In this position there would even be the maximal stimulation 

 corresponding to their maximal speed of growth in this position, 

 which is experimentally demonstrated. The experiments carried out 

 by WiESNKR, Moj.iscH ') and Czapek ') speak in favour of this theory; 

 they showed that after the tip of the radicle had been cut off, the 

 rale of growth diminished appreciably within the next 24 hours; 

 this diminution would undoubtedly have been still more apparent 

 if the observations had been recorded also during the ensuing days, 

 because the growth during the first day must still have been influ- 

 enced by the stimulus received before the amputation of the tip. 



It is generally assumed that the stimulation by gravitation depends 

 upon the pressure of the specifically heavier starch-grains (statoliths) 

 upon the outer layer of the protoplast of certain cells (stalocysts) ; 



') Reizwirkung bei Rektipetalitat und bei senkrechtera Wachstum ; Jahrbiicher 

 fur wissenschat'tliche Botanik, 1922, Bd. 61, p. 590. 

 3) Berichte d. d. bet. Gesellschaft, 1883, Bd. 1. p. 362. 

 3) Jahrb. fiir wiss. Botan., 1895, Bd. 27, p. 246. 



12 

 Poceedings Royal Acad. Amsterdam. Vol. XXVI. 



