62B 



Ci.AKK also paid attcnlioii lo bikiteral illuniiiiatioii and since his 

 results differ fi'oni my own, I made a series of observations, collected 

 here in table IX, for special comparison with his figure 7. This 

 table refers to successive illumination from two sides with an intensitj 

 of 16 candle metre power. After the first exposure the plants were 

 turned throngh 180° and illuminaled from the opposite side. It is 

 found that as long as a certain interval elapses between the beginning 

 of the two stimuli, each is expressed independently. If for instance 



T A B L E IX. 

 Successive illumination from tivo sides. 



Duration of the 



first 



exposure. 



Duration of tlie second exposure 



10 sec. 30 sec. 60 sec. \ 90 sec. 180 sec. 600 sec. 



Intensity of both exposures 16 candle metre power. 



-\- signifies curvature in the direction of the first illumination. 



— signifies curvature in the direction of the second illumination. 



the illumination is first for (iO sec. from one side, and is then 

 followed at once by the same quantity of energy from the o])posile 



T A B L E X. 

 Unilateral illutnination followed by omnilateral after-illumination. 



Intensity of fore- and after-illumination 12 candle metre power. 

 + signifies curvature in the direction of the first (unilateral) illumination. 

 ,-!- signifies curvature in a direction opposite to that of the first illumination, 



