ii4 Elementary Plant Physiology. 



and shoot. What connection is shown with the habit of 

 growth of the plant ? 



123. Prophototropism. Germinate a number of seeds 

 of oats or wheat in a shallow dish of moist soil, and, when the 

 leaves begin to appear, set in a cardboard box. Cut a circu- 

 lar hole in one side of the box, at the level of the seedlings. 

 Roll up a sheet of paper into a tube, and fasten to the box in 

 such manner that light enters through the tube only. Cover 

 the box to exclude light, except through the tube. Note the 



Fig. 83. Phototropic chamber. /, tube through which light enters. After 



Schleichert. 



position of the leaves a day or two later. In this instance 

 the leaves are placed with their apices directed toward the 

 source of the rays of light, with their axes parallel to the rays. 



124. Diaphototropism. Place in a pot a Malva, Heli- 

 anthus, or Geranium grown in the open air, and place near a 

 window with a southern exposure. Note the position assumed 

 by the younger leaves a few days later. How does this reac- 

 tion compare with that shown by leaves of grasses? 



The same form of reaction may be seen if a leafy shoot of 

 sunflower is bent down to a horizontal position and fastened. 

 Note the position of the leaf blades before and two days after 

 the operation. 



