CHAI-. V. EPINASTY AND HYPONASTY. 275 



was reversed and the shoot became more hooked. During 

 the night, after 10.40 P.M. to 8.15 A.M. on the 15th, the hook 

 again opened or straightened itself. By this time the glass 

 filament had become so highly inclined that its movements could 

 no longer be traced with accuracy ; and by 1.30 P.M. on this same 

 day, the crown of the former arch or hook had become perfectly 

 straight and vertical. There can therefore be no doubt that the 

 straightening of the hooked shoot of this plant is effected by 

 the circumnutation of the arched portion that is, by growth 

 alternating between the upper and lower surface, but prepon- 

 derant on the lower surface, with some little lateral movement. 



We were enabled to trace the movement of another straight- 

 ening shoot for a longer period (owing to its slower growth and 

 to its having been placed further from the vertical glass), namely, 

 from the early morning on July 13th to late in the evening of the 

 16th. During the whole daytime of the 14th, the hook straight- 

 ened itself very little, but zigzagged and plainly circumnutated 

 about nearly the same spot. By the 16th it had become nearly 

 straight, and the tracing was no longer accurate, yet it was 

 manifest that there was still a considerable amount of movement 

 both up and down and laterally; for the crown whilst con- 

 tinuing to straighten itself occasionally became for a short time 

 more curved, causing the filament to descend twice during the 

 day. 



timitlria Pfundii. The stiff terminal shoots of this Legu- 

 minous water-plant from Africa project so as to make a rectangle 

 with the stem below ; but this occurs only when the plants are 

 growing vigorously, for when kept in a cool place, the summits 

 of the steins become straight, as they likewise did at the close 

 of the growing season. The direction of the rectangularly bent 

 part is independent of the chief source of light. But from 

 observing the effects of placing plants in the dark, in which 

 case several shoots became in two or three days upright or nearly 

 upright, and when brought back into the light again became 

 rectangularly curved, we believe that the bending is in part 

 due to apheliotropism, apparently somewhat opposed by apogeo- 

 tropism. On the other hand, from observing the effects of tying 

 a shoot downwards, so that the rectangle faced upwards, we are 

 led to believe that the curvature is partly due to epinasty. As 

 the rectangularly bent portion of an upright stem grows older, 

 the lower part straightens itself; and this is effected through 

 hyponasty. He who has read Sachs' recent Essay on the vertical 



