248 PRACTICAL BOTANY. 



then removed. After three or four hours, remove the 

 top, and observe that the plants have turned towards the 



light. They are pos- 

 itively heliotropic. 



b. Grow seedlings 

 of Mustard in damp 

 sawdust until they 

 are well started. 

 Remove them from 



FIG. 174. Dark box for experiments in helio- ^Q sawdust and 

 tropisra. (After Schleichert.) 



support them by 



means of bent wire, carrying thin pieces of cork, just above 

 the surface of water in a beaker. Holes should be made 

 in the cork, and each seedling should be placed with its 

 radicle pointing downwards in the hole, and then secured 

 with asbestos fiber. Set the beaker in a box arranged 

 as in a. After several hours of exposure to the light 

 admitted by the hole in the side of the box, examine and 

 record your observations. 



c. Observe the positions of the leaves of various house 

 plants at different hours of the day. Do their positions 

 bear any relation to the direction from which the light 

 comes ? 



d. Observe the tendrils of Grapevines, Virginia Creeper, 

 and other climbing plants. They are negatively helio- 

 tropic, and turn away from the sun towards the support- 

 ing wall. 



30. Study hydrotropism. Provide a wooden box eight 

 or ten inches long and two inches deep, and without a 

 bottom. Tack mosquito netting over the bottom. Spread 

 on this a thin layer of sawdust, and place Beans and Peas 

 that have been soaked in water for twelve hours on this. 

 Fill the box with sawdust, and hang it at an angle of 40 

 or 50 with the horizon. Keep the sawdust damp by an 

 occasional spraying and in an atmosphere that is neither 



