LABORATORY STUDIES 131 



0') 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 (i). Note the effect on the main 

 and lateral roots and stem. 



(k) Plant seeds of Indian corn or beans 1 or 2 

 cm. 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 

 a few days the roots will emerge from the soil into the 

 air in response to the stimulus of gravity, while the menuiT."" 

 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 khnostat, 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 he made by removing 

 the longer hand of a clock and fastening to the 

 Fig. 57.— Geo- pinion a stiff horizontal wire, supported, if need 

 menrcJ). ^^^^"" bc, 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 gcotropic 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 



