748 minnesota botanical studies. 



Helianthus. 



Experiment 14- — A young specimen of Helianihus, 40 cm. iji 

 height, was placed in the dark chamber in the normal upright 

 position. Twenty-four hours later the leaves were noticeably 

 curved downward, and 72 hours later the apices of all the 

 younger leaves were pointing vertically downward. The 

 change was not so marked in more mature organs. The same 

 result was obtained by Vines (V, p. 422, fig. 8). 



Experiment 15. — A young normal specimen of Helianthus was 

 placed in a horizontal position with the stem bound firmly to a 

 stick to prevent curvatures of anything except the leaves. 

 Seventy- two hours later the leaves exhibited epinastic curva- 

 tures, pointing toward the root, in a manner generally similar 

 to that described by Vines (V, p. 429), except that all were 

 pointed in a basipetal direction. All the positions assumed by 

 leaves previously extending horizontally from the stem were 

 such that the dorsal surfaces were uppermost. 



Experiment 16. The plant used in Exp. 15 was allowed tore- 

 cover normal attitude and condition in sunlight, and then it was 

 placed in an inverted position in the dark chamber. Forty 

 hours later the leaves began to curve upward toward the roots, 

 and the curvature became more pronounced 20 hours later. 



Experiment 17. — A young normal plant of Helianthus was at- 

 tached to a clinostat and rotated with its axis in a horizontal 

 plane. During its rotation light was admitted at right angles 

 to the stem. Twenty-four hours later the leaves were curved 

 toward the root in such manner that the dorsal surfaces re- 

 ceived the rays at right angles. 



Experiment IS. — A young plant of Helianthus was placed in 

 normal upright position until the leaves were epinastically 

 curved. The plant was then inverted and illumination was 

 then given from below, with the result that in four days the 

 leaves had returned to their usual positions with respect to the 

 stem, and with their dorsal surfaces at right angles to the rays. 

 The results of the entire group of experiments agree with 

 those obtained by Vines. The leaves of Helianthus are dia- 

 heliotropic, diageotropic, and epinastic. 



