I'uder natural conditions, the leaves are hardly ever exposed 

 to direct sunlight while still in the sleep position. The diffuse 

 light of the day, preceding sunrise, would be sufficient to induce 

 the expanded condition. 



The first experiment upon the plant in question was to 

 determine the time required for a leaf to pass from the sieep 

 pof-ition into the position taken in intense sunlight. The lateral 

 Ic.ifets were selected for experiment rather than the terminal 

 one as the extreme intense sunlight position was much more 

 easily determined. It w^as not an easy matter to tell just when 

 thf terminal leaflet had finished its upward bend, but in the 

 laterals no further motion was possible as soon as the surfaces 

 came in contact. The experiment was set up by covering the 

 plant with a box the night before and then uncovering it sud- 

 denly during the period of greatest sun intensity. The leaflets 

 being in the sleep position, had considerably over ninety degrees 

 tc' travel in order to reach the vertical position. From ten to 

 fifteen minutes elapsed before any response was noticeable, but 

 when the leaflets had reached the horizontal position, their mo- 

 tion was rapid, since they reached the extreme vertical position 

 by the end of thirty minutes. The greater part of the motion, 

 therefore, was accomplished during the latter half of the time. 

 If leaves in the expanded condition were used at the beginning 

 of the experiment, the time required for lateral leaflets of young 

 leaves to attain extreme edgewise position w^as found to be nine 

 minutes. An older leaf required twelve minutes. In large plants 

 with large leaves, long since mature, the time required may be 

 as much as twenty to thirty minutes. It. generally happens in 

 such plants that the lateral leaflets do not come into actual con- 

 tact, though thev mav. reach a very acute angle. 



