Ylhite Li^ht 



Ore en Light 



Red Light 



Blue Light 



Darkness 



Series I 



Series 2. 



Series 3. 



Tbxt-fig. 2. — Diagram representinq; pliototropism of Coiivoluta roscoff- 

 ensis. Tlie circles represent ffround-plaiis of shallow porcelain vessels 

 containing a central heap of sand, a little sea water, and many Convolutas 

 (represented by daslies). The break in the circle (Series 1) indicates the 

 position of the window in a blackened bell-jar placed over each porcelain 

 vessel. The arrows outside the circles represent the direction of the 

 light. Series 1 shows the disposition of Convoluta at the time of removal 

 of the covers. Series 2 shows the instant negative phototropic reaction 

 set up by removing the covers (raising the light-intensity). Series 3 

 (only one example shown) shows the recovery (a few seconds after Series 

 2) of the positive pliototropism. The green light was produced by 

 passing daylight through three of Baker's green gelatine dims; the red 

 by using three of Baker's red films ; the blue by using four of Kirchinauu's 

 blue films and one green film. (The blue and green lights were not abso- 

 lutely monochromatic.) 



