18 



Göte Turesson 



direct sunlight the time required to blacken a sensitive photographic paper in a 

 shade that agreed with a dark-coloured paper previously made was noted. The 

 shortest time recorded during the period o£ the experiments was 6 seconds; in this 

 case the light intensity receives a value of 6, etc. — The results of two experi- 

 ments with cultures of A. prostratum that had been standing in the dark room for 

 some time have been brought together in Table VI. The plants were covered with 

 bell jars to lessen transpiration. Moreover the cultures were turned 90" every 15 

 min. to counteract heliotropic curvatures. The light intensity amounted to 10 at 

 the beginning of the experiment but sank down to 15 at the end. 



Table VI. Atriplex prostratum. 







0 min. 



60 



120 



18 0 



240 



300 



Final 

 position 



Deviation 



1 



nj^per angle 



64, 66 



±0,-4 



±0, ±0 



-8, -2 



— 7, -4 



-4,-8 



50, 48 



— 14, — 18 



lower angle 



87, 62 



+ 8, +Ö 



-1,-4 



- 1, + 0 



-1, ± 0 



-2,-2 



84, 62 



+ 8, ± 0 



2 



upper angle 



61, 79 



-4,-2 



- 1, + 0 



±0,-7 



-3, + 0 



-4,-2 



49, 68 



- 12, - 11 



lower angle 



90, 43 



+ 4, -f 1 



-1,-6 



— 2 —2 



±0, ± 0 



— 1, ± 0 



90, 50 



±0,-7 



Table VII. Atriplex prostratum. 







0 min. 



60 



120 



180 



24 0 



Final 

 position 



Deviation 



1 



upper angle 



15, 25 



- 3, ± 0 



- 3, - 2 



± 0. ± 0 



± 0, ± 0 



9, 23 



-6,-2 



lower angle 



79, 60 



± 0, ± 0 



-4, - 1 



- 2, ± 0 



±0,-1 



85, 62 



-6,-2 



2 



upper angle 



77, 80 



-2,-2 



±0,-1 



±0, — 2 



- 1, ± 0 



74, 75 



-3,-5 



lower angle 



104, 80 



± 0, + 2 



±0,-4 



±0,-2 



± 0, ± 0 



104, 84 



±0,-4 



The apical regions of the branches already appreciate during the first 60 min. 

 the change in light intensity, just as is the case in a removal from light to dark- 

 ness; they bend downwards while the basal parts continue for some time to move 

 upwards on account of the after-effect folloving on the negative geotropism induced 

 during the time the plants were darkened. The base of the branch does not begin 

 to participate in the movement which is bringing down the whole branch into a 

 horizontal position until this geotropic stimulus has died out and the latent period 

 has been passed. Table VII shows the progress of the curvature in plants ex- 

 posed to a light intensity of 9 — 11. A remarkable difference is seen in the rate 

 of the downward movenient in the plants listed in tables VI and VII. That the 

 downward movement in the plants of table VII does not proceed as rapidly as 

 that seen in table VI is probably due to the fact that growth is retarded at higher 

 light intensities. Additional evidence to show that these movements are true sti- 



