39 



phototropic and geotropic phenomena among the modified 

 natations. 



Height of plants. 



The length of the ^Irewa-coleoptiles has no influence 

 upon the magnitude of the geotropic presentation-time, 

 provided that the dimensions of the coleoptiles lie betwee'n 

 10 and 35 mm. This was verified by preliminary experi- 

 ments made for this purpose and agrées perfectly with the 

 results of B 1 a a u w ') as to the phototropic presentation-time. 



Age of plants. 



With a single exception only plants of 4 days old were 

 used ; the seeds were soaked for two of thèse four days 

 and were then grown in the zinc vessel for 2 days more. 

 Plants of 5 days old were used exceptionnally. A séries 

 of preliminary experiments showed no différence between 

 plants 4 days old and others 5 days old. 



Position of plants. 



Rotherf*) says, speaking of the direction, in which 

 the coleoptile is stimulated: „Trotz seiner deutlich dorsiven- 

 tralen Structur verhâlt sich der Cotyledo ^) physiologisch 

 wie ein radiâres Organ ; wenigstens beobachtete ich keine 

 merklichcn Differenzen der Krummungsfâhigkeit in Ab- 

 hângigkeit davon, welche Seite des Cotyledo der Licht- 

 quelle zugekehrt war." Blaauw *) too regards the 

 coleoptile of A oena „physiologically" circular. This however 

 is not quite the case, although the différence is only a 

 slight one. 



The geotropic presentation-time was found a little shorter 

 when stimulating in the direction of the short axis of 

 the elliptical apex than in a direction perpendicular to 



1) A. H. Blaauw, 1909, p. 12. 



2) W. Rothert, 1894, p. 30. 



3) So the coleoptile is named by Rothert. 



4) A. H. Blaauw, 1909, p. 11. 



