$2 EXPERIMENTAL PLANT PHYSIOLOGY. 



Plant seeds of the Pea, Bean, or Corn in the sawdust. The roots 

 FIG. 45. pass through the meshes downward and the 



shoots upward. Invert the apparatus and these 

 organs will bend in the opposite directions. 

 (Fig. 450 



FIG. 46. 



Geotropism of roots and Apogeotropism of leaves of Onion, 



shoots. (After Oels.) (Frank.) 



EXPERIMENT 61. 



APOGEOTROPISM. 



Place a Tulip, Hyacinth, Onion, or Fritillaria, which is growing 

 rapidly, in a horizontal position. In a short time the leaves curve 

 directly upward. (Fig. 46.) 



EXPERIMENT 62. 



DIAGEOTROPISM. 



Observe the opening flower-buds of a Narcissus, which at first are 

 erect, but later the perianth-tube assumes a horizontal position. 

 After they have attained this position lay the pot on its side with 

 the leaves and stems horizontal and the perianth-tube pointing 

 downward. In 10 hours the pedicels will have again curved to 

 place the perianth-tube in the same position as before. 



43. Perceptive and Motor Zones of Roots. The stimulus of 

 gravity is received by a sensitive portion near the tip of a root 

 (the perceptive zone), and an impulse is conveyed to a region 

 several millimeters distant which curves (the motor zone). 



