218 



EXPERIMENTS WITH PLANTS 



place themselves vertically (i. e., parallel to the light) 

 will be found in the morning and afternoon with their 

 faces, perpendicular to the light; in this way they fol- 

 low the sun all day, facing 

 eastward in the morning and 

 westward in the afternoon 

 (plants of the Pea family, 

 some Mallows, etc. ) . What 

 coirimon plants do this ? 

 Study Clovers, Lupins , 

 Melilotus, etc. Notice the 

 cushion - like joints, or 

 hinges, on which the leaves 



124. Acacia leaf, night or sleep position. tum. 



Study the "sleep -position" of leaves at night in 

 Oxalis, Clover, Acacia (Figs. 124 and 125), also in 

 seed-leaves of Sunflower, Squash, etc. This position 

 may be of advantage 

 in reducing evapora- 

 tion or in diminish- 

 ing the loss of heat, or 

 both. It may in many 

 cases be produced 

 artificially by putting 

 the plants in dark- 

 ness for a time dur- 

 ing the day (Oxalis, 



AcaCia, ClOVer, etc) . 125. Acacia leaf, day position. 



