LABORATORY STUDIES 131 
(j) Grow a bean seedling in water culture until some of the 
horizontal roots have developed a little way. Then place the 
main root horizontally as in (¢). Note the effect on the main 
and lateral roots and stem. 
(k) Plant seeds of Indian corn or beans 1 or 2 
em. beneath the surface of the soil, in a completely 
filled flower pot. Fasten a coarse wire netting over 
the top of the pot, and invert it, putting it on an 
iron tripod, standing in a plate of water, and place a 
bell jar over the whole, to keep the air moist. After 5, 5. 
a few days the roots will emerge from the soil into the — Geotrop- 
air in response to the stimulus of gravity, while the cGy" 
stems grow on up into the soil. 
(l) Place a flower pot with a growing plant in a horizontal 
position. At the same time place another one with a similar 
plant horizontally in a klinostat, so that it rotates slowly with 
the axis of rotation horizontal. Keep both in a dark room 
twenty-four hours during the process, and then compare the 
plants. (A klinostat is an apparatus worked by clock-work, 
which rotates a flower pot fastened to it at a 
slow rate, being arranged so that the axis of 
- rotation may be in any direction desired. A 
simple klinostat can be made by removing 
the longer hand of a clock and fastening to the 
gis. 87.—Goo- pinion a stiff horizontal wire, supported, if need 
cont (D. —— be, at the other end. At the middle of the 
wire may be placed a large cork, to which seed- 
lings can be attached. With a small clock it is impossible to 
use a flower-pot, as it is too heavy, and so instead the seedlings 
will be fastened to the edge of the cork, and since they are 
exposed to the stimulus of gravity from successively different 
directions, they will show no geotropic curvature. In home- 
made apparatus of this kind the portion including the cork 
with the attached plants ought to be so enclosed that the plants 
will not dry out.) 
(m) Place seedlings at the edge of a horizontal wheel that 
can be rotated very rapidly (centrifugal apparatus). When the 
centrifugal force much exceeds the force of gravity, the roots 
will grow almost directly outward and the stems almost directly 
inward. If both are equal, the roots will be directed downward 
and outward at an angle of 45 degrees, and the stem upward 
