Botany. — "Further researches on the antiphototropic curvatures 

 occurring in the coleoptiles of Avena." By Dr. C. E. B. 

 Bremekamp. (Communicated by Prof. F. A. F. C. Went.) 



(Communicated at the meeting of May 27, 1922). 



As I liave shown in my former communication ^), the conditions 

 under which the coleoptiles of Avena produce an antipholotropic 

 curvature, may be summed up in this way: 



1^"^. At the end of the one-sided illumination the rate of growth 

 should have about the same value at both sides of the coleoptile^). 

 This result is only to be obtained with light of rather strong inten- 

 sity. If this is provided for, the product of the intensity and the 

 exposition-time should exceed a certain value. 



2"*^. After the close of the illumination, there should be a more 

 rapid increase of the growth-rate, in the side that has received the 

 greatest quantity of light. In this way it should reach here a higher 

 value. 



An explanation of the way wherein a difference in the rate of 

 increase may come about, was given in my paper entitled : "Theorie 

 des Phototropismus" '). After a previous diminution in consequence 

 of the illumination, the rate of growth after some time increases 

 again. This process commences probably the sooner, according as 

 the diminution has been the greater. In this way the increase of 

 the growth-rate in the side which has received the greatest quantity 



C. E. B. Bremekamp. On anliphototropic curvatures occurring in the coleo- 

 ptiles of Avena. Proceedings Kon. Akad. v. Wetensch. te Amsterdam. Vol. XXIV, 

 p. 177. 1921. 



2) In my previous work in stead of the expression "the rate of growth at the 

 end of the illumination" I used the ampler expression "the rate of growth 

 belonging to the grade of sensibility existing at the end of the illumination". In 

 this way I reckoned with the possibility that it would give a latent period between 

 the phototropical reaction i.e. the change of the rate of growth, and the absorption 

 of the light with its influence on the sensibility. However, a critical examination 

 of the literature on this subject, has convinced me that the evidence in favour of 

 the existence of this latent period, is not conclusive. The investigations of Bose 

 and others have made it very probable that the reaction follows the illumination 

 almost immediately. 



*) C. E. B. Bremekamp. Theorie des Photolropismus. Ree. d. trav. bot. Néer- 

 landais Vol. XV. p. 123. 1918. 



