100 Kansas Academy of Science. 



Schaffner says that the Helianthus annuus begins to nutate 

 toward the east before the morning light could affect it. The 

 Melilotus alba, however, moves only when acted upon by light. 

 It will remain constant for days facing one direction if the light 

 comes from that direction. It will change the position of its leaves 

 very quickly if the direction of the incident ray is changed. 



After these points were determined, an attempt was made to dis- 

 cover, if possible, the relation ■existing between the rate of move- 

 ment and the strength of the light. Several methods were used in 

 these experiments. Some healthy potted plants were placed in the 

 laboratory window. The leaves soon all turned their faces to the 

 light. The pot was then turned half-way round. The leaves then 

 twisted on their pulvini, rose or fell, the stem changed its curve, so 

 that in about thirty minutes to one hour the leaves were all again 

 facing the light. 



The easiest movement, judging from the time required, was a 

 twist at the pulvinus. The second was where the leaf merely fell 

 or dropped down. The one requiring the most time was where the 

 leaf had to rise against gravity. This latter movement was accel- 

 erated when the leaf was lifted either by the wind or one's finger. 

 This accounts for the sudden jumps which will be seen in the record 

 of the movemerit of leaves taken when the wind was blowing. 



Second method : A box sufficiently large not to touch the plant 

 was taken, one end removed, and the inside lined with dark paper. 

 This was then placed over a plant in the field, with the end left 

 open. The light thus came to the plant from one direction only. 



In some experiments the box was left over the plant during the 

 night, facing the west, so that the leaves in the morning faced 

 west. The box was then removed and the morning sun shone on 

 the plant. The leaves quickly faced about to the east. Other ex- 

 periments were made by placing the box over the plant at eight 

 o'clock A. M., so that the light came from the west. The leaves at 

 this time were all turned to the east, but they turned in a short 

 time to the west. 



The same results were secured by letting sunlight fall on the 

 plant from the east at five o'clock in the evening, or by letting the 

 light come from the north at noon. It was found, however, that, 

 if the box was left over a plant for two days, those leaves which 

 were in the dark part of the box, and were therefore not very 

 strongly illuminated, were not able to recover from the sleep posi- 

 tion the morning of the third day, even when exposed to the morn- 

 ing sunlight for two hours. 



