564 LIFE MOVEMENTS IN PLANTS 



demonstrate the causal relation between temperature vari- 

 ation and diurnal movement, of which the two additional 

 tests described below offer further confirmation. 



REVERSAL OF NORMAL RHYTHM. 

 The normal diurnal movement is, as we have ^een, a 

 fall during rise of temperature from morning to afternoon, 

 and a rise from afternoon till next morning. I succeeded 

 in reversing the normal rhythm of Basella by reversing 

 the normal variation of temperature at the two taming 

 points, in the morning and in the afternoon. The plant 

 was subjected to falling temperature in the morning and to 

 rising temperature in the afternoon. The normal movement 

 now became reversed, i.e., an erection instead of fall in ihe 

 forenoon and a fall instead of rise in (he afternoon (p. 28). 



EFFECT OF CONSTANT TEMPERATURE. 



The second test which I shall employ is the effect of 

 maintenance of constant temperature, which should wipe off, 

 as it were, traces of periodic movement. It was necessary 

 for this investigation to maintain the plant chamber at 

 constant temperature throughout day and night. The usual 

 thermostat is virtually a recess in a double-walled 

 chamber filled with water, the chamber being covered 

 with a heat insulating material. But this contrivance is 

 unsuitable for the plant chamber which is to contain 

 good sized plants, and the recording apparatus. The 

 problem of maintaining a large air-chamber at constant 

 temperature presented many difficulties which were ulti- 

 mately overcome by the device of an extremely sensitive 

 thermal regulator. 



The Thermal Regulator. — I shall in a future paper give 

 a complete account of the large thermostatic air-chamber. 

 The important part of the apparatus is an electro-thermic 

 regulator which interrupts the heating electric current as 

 soon as the temperature of the chamber is raised a 



