Day: position of dorsi ventral leaves. 745 



exercised that the leaves had assumed their final position and 

 balance of growth. This last precaution is quite essential 

 since many radical leaves are hyponastic in earlier stages, and 

 epinastic in later stages of development. At the end of each 

 experiment the condition of the plant was noted, and if it was 

 unhealthy or flaccid, results were disregarded. In every in- 

 stance duplication of the experiment was made. The dark 

 chamber used was constructed of zinc and was placed in the 

 plant house in such position that the sunlight could not strike 

 it. The temperature varied between 24° and 28° C. 



DETAIL OF EXPERIMENTS. 



Experiment 1. — A normal specimen of a rosette of Taraxacum 

 obtained by germination of a seed three months previously was 

 placed in an upright position in a dark chamber. Twenty-four 

 hours later the younger leaves had begun to curve upward. 

 Forty-eight hours later all the leaves were pointing upward. 

 The vertical position might be due to hyponasty, or negative 

 geotropism. 



Experiment 2. — A specimen of Taraxacum, similar to that 

 used in Exp. 1, was attached to the clinostat in a dark chamber 

 in such manner that the axis of the root-stock was rotated 

 while held in a horizontal position. Forty- eight hours after 

 the beginning of the experiment, the leaves had assumed a 

 position parallel to the axis of the root-stock. The position of 

 the leaves in this instance was clearly due to hyponasty. 



Experiment 3. — A specimen of Taraxacum was placed in the 

 dark chamber with the root-stock in a horizontal position. 

 Forty- eight hours later all of the leaves were at right angles 

 to the root-stock and pointing upward. At the beginning of 

 the experiment eight leaves held this position, and the same 

 number were pointing in an opposite direction. In order to 

 assume the upright position the last group moved through an 

 arc of 180° In this, as well as all other experiments, no ac- 

 count was taken of torsions. 



Experiment 4- — A specimen of Taraxacum was placed in the 

 dark chamber in an inverted position, with the root-stock 

 pointing upward, and the leaves horizontally with their dorsal 

 surfaces below. Forty-eight hours later all of the leaves had 

 curved upward into a position parallel with the root stock. 



