66 PRACTICAL COURSE IN BOTANY 



EXPERIMENT 45. To SHOW THAT ROOTS SHUN THE LIGHT. Cover the 

 top of a glass of water with thin netting, arid lay on it sprouting mustard 

 or other convenient seed. Allow the roots to pass through the netting into 

 the water, noting the position of root and stem. Envelop the sides of 

 the glass in heavy wrapping paper, admitting a little ray of light through 

 a slit in one side, and after a few days again observe the relative position 

 of the two organs. How is each affected by the light ? 



EXPERIMENT 46. To FIND OUT WHETHER ROOTS NEED AIR. Remove 

 a plant from a porous earthenware pot in which it has been growing for 

 some time ; the roots will be found spread out in contact with the walls 

 of the pot instead of embedded in the soil at the center. Why is this ? 



EXPERIMENT 47. To SHOW THAT ROOTS SEEK WATER. Stretch some 

 coarse netting covered with moist batting over the top of an empty tumbler. 

 Lay on it some seedlings, as in Exp. 45, allowing the roots to pass through the 

 meshes of the netting. Keep the batting moist, but take care not to let 

 any of the water run into the vessel. Observe the position of the roots 

 at intervals, for twelve to twenty-four hours, then fill the glass with water 

 to within 10 millimeters (a half inch, nearly) or less of the netting, let 

 the batting dry, and after eight or ten hours again observe the position 

 of the roots. What would you infer from this experiment as to the affin- 

 ity of roots for water ? 



EXPERIMENT 48. WHAT BECOMES OF THE WATER ABSORBED BY ROOTS. 

 Cover a calla lily, young cornstalk, sunflower, tropseolum, or other 

 succulent herb with a cap of oiled paper to prevent evaporation from the 

 leaves, set the pot containing it in a pan of tepid water, and keep the tem- 

 perature unchanged. After a few hours look for water drops on the leaves. 

 Where did this water come from ? How did it get up into the leaves ? 



EXPERIMENT 49. To SHOW THE FORCE OF ROOT PRESSURE. Cut off 

 the stem of the plant 6 or 8 centimeters (3 or 4 inches) from the base. 

 Slip over the part remaining in the soil a bit of rubber tubing of about 

 the same diameter as the stem, and tie tightly just below the cut. Pour 

 in a little water to keep the stem moist, and slip in above, a short piece 

 of tightly fitting glass tubing. Watch the tube for several days and note 

 the rise of water in it. The same phenomenon may be observed in the 

 " bleeding " of rapidly growing, absorbent young shoots, such as grape, 

 sunflower, gourd, tobacco, etc., if cut off near the ground in spring when 

 the earth is warm and moist. By means of an arrangement like that shown 

 in Fig. 81, the force of the pressure exerted can be measured by the dis- 

 placement of the mercury. This flow cannot be due to the giving off of 

 moisture by the leaves, since they have been removed. Their action, 

 when present, by causing a deficiency of moisture in certain places may 



