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, and 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, tropzolum, 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, ete., 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 
