University Studies 



Vol. V JULY 1905 No. 3 



I. — On the Movements of Petals 



BY ESTHER PEARL HENSEL 



INTRODUCTION 



The following paper has to do with an investigation of the 

 physical causes which bring about opening and closing move- 

 ments, periodic or otherwise, of certain flowers. With that end 

 in view, seven different species of flowering plants have been ex- 

 perimented upon directly, a much larger number being simply 

 observed with respect to the nature, time, etc., of their antho- 

 tropic movements. 



Movement consists in the corolla taking upon itself either the 

 open or closed position for certain periods of the day or night; 

 for example, the morning glory (Ipomoea purpurea) opens early 

 in the morning (from 4:00 to 5:00 a.m., in the greenhouse) and 

 closes from 11:00 a.m. to 2:00 p.m., or even 5:00 p.m. on cool 

 days, while the common dandelion (Taraxacum taraxacum) 

 opens from 7:00 to 8:00 a.m. and closes from 5:00 to 6:00 p.m. 



In the closed position, the petals or florets may assume prac- 

 tically the same position as that of the bud, as in the gentians^ 

 asters, dandelions, etc. ; often, however, the edges of the petals 

 only touch, forming a dome inside of which the stamens and 

 pistil are well protected, as in the wild rose and in the tulip. In 



University Studies, Vol. V, No. 3. July 1905. 



