II] 



HABITS OF CONVOLUTA 



53 



Fig. 12. Tropistic reaction of Convoluta roscoffensis to Monochro- 

 matic Light. Each circle represents a ground-plan of a shallow 

 porcelain vessel containing a central heap of sand, a little sea- 

 water, and many Convolutas (represented by dots). 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 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 phototropism. The green 

 light was produced by passing daylight through three of Baker's 

 green gelatine films ; the red by using three of Baker's red films ; 

 the blue by using four of Kirchmann's blue films and one 

 green film. (The blue and green lights were not absolutely 

 monochromatic.) 





