On the Movements of Petals 



35 



Variations in the amount of light present do not seem to affect 

 closing-, for, when a plant with open flowers is put into the tin 

 box with increased temperature, and practically no light, except 

 the small amount from the non-luminous alcohol flame, closing 

 occurs as readily as in the open, if not more so. Opening and 

 closing also occur as in the open when the plants are put in the 

 black shade tents. Closing may take place at as low a degree 

 of temperature as 7.5° C, when the flower has been kept open 

 beyond its usual time by several hours, as in the case cited on 

 page 34, for February 2, 1905. This is to be explained on the 

 basis that, since the flower's existence is normally only one day 

 or a part of it, the flower has remained open its usual time ac- 

 cording to its hereditary habits, its activities were completed, and 

 hence closing occurred. Whenever closing occurs in the morn- 

 ing between 11:00 and 12:00, the temperature is nearly always 

 19° to 26° C, while, when it is delayed until 2:00 to 4:00 p.m.^ 

 it is as low as 13° or 17° C. with high humidities, showing that 

 it is not the extremely low temperature, but the constantly low 

 temperature, continued for a considerable time, which is the 

 cause of the late opening. 



SUMMARY 



I have been able to control the opening and closing of dande- 

 lion flowers in so far that I can close them permanently with 

 lower temperature than normal, and open them when tempera- 

 ture has continued too jOw, by the application of either dry or 

 moist heat. It is also possible to close any ephemeral flower be- 



225 



