1&9 



of light, may gain an advantage of tiiat in the other side. This 

 advantage will be the greater, according as there lies more time 

 between the moment whereon the growth-rate in the anterior side 

 has reached its lowest valne, and ilie moment whereon this is the 

 case in the posterior side. If it is sutTiciently great, the rate of growth 

 in the first-named side with the aid of it will reach at the end of 

 the illumination oi' shortly afterwards a higher value. In any case the 

 exposition-time should be long enough that an advantage of sufficient 

 extent may be gained. 



However, in my previous communication t showed that an anti- 

 phototropic curvature may come about also, if the expositiontime 

 is very short. As in this case the explanation given above naturally 

 fails, 1 suggested that the theory of Bosk ^) might give us here the 

 clue to get out of the difficulty. 



According to this theory, a disturbance of equilibrium in the 

 organism generally manifests itself in a local contraction (the direct 

 effect) which is accompanied by an expansion in the adjoining tissue 

 (the indirect effect). In the latter, the turgescence would be heightened 

 by the water expelled from the contracted portion, and accordingly 

 a temporary enhancement of the growth-rate would be the result. 

 In this waj^ a normal curvature in one part of an organ would 

 always go together with an antitropic one in the adjoining region. 

 Only if an increase of the rate of growth in that part, should be 

 impossible, the antitropic curvature would remain out. In our case 

 then, the origin of the antiphototropic curvature in the tip of the 

 coleoptile might be connected with the origin of a normal photo- 

 tropic curvature in the basal part. 



To test the correctness of this supposition, I made a number of 

 experiments wherein the phototropic reaction of coleoptiles exposed 

 in the whole of their length, was compared with the reaction of 

 coleptiles illumiiuited at the tip only, or illuminated also in the 

 whole of their length, but after an exposition of the basal part to 

 a two-sided illumination of rather great strength. 



Before I enter into the details of these experiments, I will give 

 a survey of the results which previous investigators have obtained 

 in their researches on the infiuence of an illumination of one part, 

 on the phototropic reaction of another. 



First of all then, we have to consider the experiments on photo- 

 tropism made by Bosk ') himself. They are rather few in number, 



M J. G. BosE. Plant Respose. London 190G. 



') J. G. BosE assisted by Jyotiprakash Sircar. The transmitted effect of photic 

 stimulation. Life Movements in Plants. Galculta 1918/19. p. 362—877. 



