THE SPERMAPHYTES. 



251 



FIG. 177. Leaf of Oxalis carnea. 1, the ordi- 

 nary day position ; 2, night position. (After 

 Sachs.) 



of Oxalis, Impatiens, or Beans during the daylight and 

 again as darkness comes on. 



b. Observe the flowers of Morning Glory, Mayweed 

 (Ma rut a cotula, 



D. C.) of the culti- 

 vated Daisy (Bellis 

 perennis) during the 

 day and again late 

 in the afternoon. 



c. In the earlier 

 part of the day place 

 an Oxalis growing 

 in a pot in a large 

 box painted black 

 on the inside and 

 from which all light 



is excluded. In two or three hours examine the posi- 

 tion of the leaves. Make similar observations by invert- 

 ing a box over Clover plants growing naturally out of 



doors. Make the 

 box light tight all 

 around. 



This change of 

 position is brought 

 about by varia- 

 tions in the 

 growth of the cells 

 on the upper and 

 under sides. In 



cases where the 



movements are most distinct, this variation in growth 

 occurs in a distinct swelling at the base of the petiole 

 known as a pulvinus. Sections through the pulvinus 

 often show a distinct difference in the size of the cells. 

 The sleep movements of plants are believed to be pro- 



FIG. 178. Leaves of a Beau, a, the day position 

 6, the night position. (After Detmer.) 



