Ampliicarpu-a monoica. 315 



results as to time of taking nyctitropic position, for usually 



the leaves remained more or less dellexed during the entire 

 day. Even on a clear day, a brisk wind or a fall in tem- 

 perature would induce the nyctitropic position at an earlier 

 hour. 



Electrical disturbances of the atmosphere seem to have an 

 effect upon Amphicarpaa. On one hot July day a heavy 

 thunder-storm occurred about 5 P.M. ; the clouds were 

 unusually heavy. Within an hour, the sky had cleared, 

 and the sun was shining brightly. Yet the plants did not 

 recover their normal position, but retained the nyctitropic, 

 which had been assumed on the approach of the storm. 

 This statement applies equally well to those plants which 

 had not suffered from the force of the rain. The sunset 

 hour was 7.30. 



So many conflicting conditions make it difficult to state 

 a general rule. As far as I am able to gather from these ob- 

 servations, there seems to be but a slight difference between 

 the time of taking nyctitropic position and sunset hour in 

 the summer months. On the other hand in the winter 

 season, the leaflets close from fifteen minutes to a half hour 

 before sunset. The rapid approach of darkness in the 

 latter case; the long twilight in the preceding certainly 

 form important factors. 



Plants in an open space, upon a clear warm day, are late 

 in taking the nyctitropic position— just about the sunset 

 time. But this statement can not be correct for the indi- 

 viduals growing in the woods. From the few studied in 

 their native haunts, the period in August (sunset about 

 7,) is from fifteen to twenty minutes earlier than this hour. 



The above facts lead to the conclusion that there is not 

 a definite time-relation between the time of nyctitropic 

 position and the exact time at which the sun sets. 



Pulvinus Structure 



The pulvini are much more pubescent than the other 

 portions of the petiole. Both the long, unicellular hair and 

 21 



