258 Darwin and Pertz . — On the Production 
the klinostat was stopped, the plant was rotated through 90°, 
so that the plane of movement was at right angles to the 
direction of incident light. Phalaris is heliotropically so 
sensitive that the impressed rhythm would be hardly per- 
ceptible without this precaution. For the sake of simplicity 
Fig. 6. 
the symbols + and — are retained after the klinostat was 
stopped ; thus during the last 15' of the fifth half-hour the 
grass was actually curving away from the light ; during the 
first half of the sixth period it is shown moving away from the 
light because its movement was a continuation of that curva- 
ture, although it was in fact moving across the line of 
light. 
