Amphicarpcea monoUa. \\ ' 



have evidently begun. Sudden changes in environment may 



accelerate movements, or indeed may cause plants to take the 

 sleep position even in the day-time. Carrying a plant from 

 the moist atmosphereof the green-house into the dry air of a 

 heated room having about the same temperature, produced 

 a shock, which resulted in the assuming of the nyctitropic 

 position. Often complete recovery did not take place until 

 the plant was returned to congenial, moist surroundings, or 

 some time thereafter. 



Exactly what may be designated as a complete nycti- 

 tropic position is still perhaps a matter of doubt. About 

 sunset the following condition may be seen : The leaflets 

 have fallen 90 , the terminal one points perpendicularly 

 downward or inclines in the direction of the petiole, the 

 surfaces of the laterals approach ; often the apices touch 



each other. 



Simple leaves also deflex 90 . When the plant is quite 

 young, after thus deflexing, the blade turns and lies with its 

 under surface below the petiole, nearly parallel with it, and 

 almost in contact with it. Thus, at this time these leaves 

 pass through 180 . (Plate XXV, Fig. 3.) This remark- 

 able movement disappears in plants having four or five 

 compound leaves, and frequently before this number is 



reached. 



Within two hours after all leaflets have assumed the posi- 

 tion described above, the terminal one rises slightly, the pul- 

 vinus forming an acute angle with the petiole. The blade 

 stands out, as shifting toward the right or left has taken 

 place. Gradually, though constantly, the leaflet turns its 

 upper surface, the pulvinus changes its angle, the leaflet 

 inclines again toward the perpendicular until about 1 1 p.m.; 

 as a result of this continuous movement, the upper sur- 

 face of the terminal leaflet lies in the same plane as the 

 surface of a lateral leaflet, and faces outward (that is to- 

 ward the observer or directly away from him— according 

 to his position in relation to the plant). (Plate XXVI.) 



The petiolar angle most commonly assumed is nearly 



