164 



the exposition-time 12, 15, 18 and 21 seconds. Tiie temperature 

 varied between 15° and 20° C, but in each series of experiments 

 it remained nearly constant. After the illumination the boxes came 

 on the clinostat. 



With an exposition of 12 seconds (light-quantity 9000 MCS), after 

 37s hours the coleoptiles exposed in the whole of their length, 

 were feebly antitropic (S-shaped), the coleoptiles exposed at the tip 

 only, feebly curved in the normal way. 



With an exposition of 15 seconds (light-quantity 11250 MCS), the 

 results were nearly the same. 



With an exposition of 18 seconds (light-quantity 13500 MCS), 

 after 372 liO"i"S the coleoptiles exposed totally, were clearly antitropic 

 (feebly S-shaped), the coleoptiles exposed at the tip only, nearly 

 straight. 



With an exposition of 21 seconds (light-quantity 15750 MCS), 

 after 372 hours the coleoptiles were all nearly straight. 



The experiment with the exposition-time of 15 seconds, was 

 repeated 5 times, always with the same result. That in this case, 

 the occurrence of an antitropic curvature at the tip of the totally 

 exposed coleoptiles, is dependant upon the exposition of the basal 

 part, cannot be doubted. 



The results of the experiments wherein the basal part of the coleo- 

 ptiles was previously exposed to a very strong illumination, and 

 where, therefore, the unilateral after-illumination of the whole 

 coleoptile did not give a normal curvature in the basal part, demon- 

 strate the significance of this influence also clearly. 



In these experiments, I compared the result of an unilateral illu- 

 mination of the whole coleoptile after a twosided exposition of the 

 basal part, with that of an unilateral illumination of seedlings previ- 

 ously kept in the dark. During the fore-illumination two screens 

 of the same shape were used, one in front of the coleoptiles, and 

 one behind them. They were prepared in the same way as those 

 used in the previous experiments, the only difference being that in 

 this case, the basal part of the paste-board was for the greater part 

 cut away. In this way during the illumination, at the lip of (he 

 coleoptiles a piece of 27, — 3 mm. remained in the dark. The fore- 

 illumination lasted 60 seconds, and during this time, every 10 seconds 

 the box was turned round. At the end of the fore-illumination the 

 box was turned round for the last time, then the screens ware taken 

 away, and the seedlings once more exposed to the same light. This 

 time the illumination lasted 12 or 15 seconds. The intensity of the 

 illumination was always 750 MC. The result of these experiments 



