Day: position of dorsiventral leaves. 747 



a position parallel to the root- stock and pointing directly up- 

 ward. 



Experiment 9. — A specimen of a rosette of Nicoiiana was 

 placed in a dark chamber, with the root-stock in a horizontal 

 position and the leaves in a vertical plane. Forty-eight hours 

 later all the leaves were pointing upward. 



Experiment 10. — A specimen of the rosette of Nicoiiana, with 

 the roots enclosed in sphagnum, was placed in a chamber in a 

 natural position and light was allowed to enter from above and 

 below, striking the under and upper surfaces of the leaves. 

 Observations from time to time during a period of six days re- 

 vealed no movements except by a few of the leaves in an effort 

 to assume a position more nearly perpendicular to the light. 



Experiment 11. — A specimen of Nicoiiana prepared with 

 sphagnum was placed in a dark chamber in an inverted posi- 

 tion, with the root-stock pointing upward and the dorsal sur- 

 faces of the leaves facing downward. One week later no 

 changes had taken place except those indicated in Exp. 10. 



Experiment 12. — A specimen of Nicoiiana prepared with 

 sphagnum was attached to a clinostat, and rotated with the 

 axis of the root- stock in horizontal, and the leaves in a vertical 

 plane. Forty -eight hours later the leaves had curved toward 

 the root, in a manner indicative of epinastic growth and exhib- 

 iting a behavior exactly contrary to Taraxacum. 



Experiment 13. — A normal specimen of Nicoiiana prepared 

 with sphagnum was attached to a clinostat and rotated with 

 the axis of the root-stock in a horizontal position, and its leaves 

 in a vertical plane. Light was allowed to strike the plant at 

 right angles to the root- stock and parallel to the surfaces of 

 the leaves. Forty-eight hours later the leaves had curved to- 

 ward the root in such manner as to exhibit their dorsal sur- 

 faces to the light as each in turn was brought opposite the 

 opening in the dark chamber. 



It maybe seen by experiments 10, 11, and 13 that the mem- 

 bers of the rosette of Nicoiiana, are diaheliotropic; by experi- 

 ment 9 that they are apogeotropic; and by experiments 9 and 

 12 that they are epinastic. The degree of irritability to the 

 three classes of stimuli decreases in the order named. 



