750 MINNESOTA BOTANICAL STUDIES. 



adaptive processes interfere in such manner as to render the 

 results difficult of interpretation. 



The foregoing experiments indicate that the leaflets of Ari- 

 saema are diaheliotropic, epinastic, and diageotropic. 



Lactuca. 



Experiment 26. — A specimen of a rosette of Lactuca scariola 

 was placed in a clinostat in a dark chamber, and rotated with 

 its root- stock in a horizontal and the rosette members in a vert- 

 ical plane. Illumination was given at right angles to the root- 

 stock. Forty- eight hours later the radical leaves had curved 

 backward and pointed toward the roots, in a manner indicative 

 of diaheliotropism. 



Experiment 27. — A specimen of the rosette of Lactuca was 

 placed in the dark chamber in an inverted position. Twenty- 

 four hours later all the leaves had curved upward toward the 

 roots. 



Experiment 28. — A specimen of Lactuca was placed in a dark 

 chamber in an inverted position and illuminated from below. 

 Pour days later no noticeable change of position had occurred. 

 Many torsions were to be seen, however. 



Experiment 29. — A specimen of the rosette of Lactuca was 

 attached to a clinostat, with the root- stock horizontal and the 

 leaves in a vertical plane. Forty-eight hours later the leaves 

 had curved toward the root. 



Experiment 30. — A specimen of Lactuca was placed in a dark 

 chamber in a horizontal position. Forty-eight hours later 

 curvatures had begun, and seventy - two hours later all the 

 leaves were pointing upward. 



The curvatures of Lactuca are diaheliotropic, epinastic, and 

 apogeotropic. 



RECAPITULATION. 



A consideration of the results of the foregoing experiments 

 leads to the following conclusions: 



I. The prevalence of an epinastic or hyponastic condition of 

 growth in any organ is due entirely to internal causes and may 

 be said to be spontaneous. In many plants leaves are epinas- 

 tic in an earlier stage of growth, and hyponastic in a later 

 one, or vice versa. The balance of the two forces may not be 

 disturbed or initiated by external conditions. Light, there- 



