GEOTROPISM. 121 



once in fifteen minutes. This may be accomplished partly by shortening 

 the hair-spring and partly by removing the alternate teeth from the es- 

 capement-wheel. A brass sleeve about an inch long, tightly fitting over 

 the spindle, is to be made, bearing at its outer end a brass disk two inches 

 in diameter, perforated with a few holes on its margin and revolving in a 

 plane parallel and close to the clock-face. A glass plate with holes for 

 the spindle and for winding should then be placed over the works, or the 

 original face may be retained. Such a clinostat will carry easily a con- 

 siderable weight in a vertical plane, and a five-inch pot when revolving 

 horizontally. In the latter case a saucer or crystallizing-dish must 

 always be placed beneath the pot to prevent water from running from 

 the pot into the works. The clock will need winding once in two days, 

 and while the cork is removed for the purpose, it should be kept slowly 

 revolving in the hands. 



The result of an earlier experiment (No. 46) showed that 

 side roots are guided, though in a different direction, by the 

 same influence which guides the main root. The question 

 now arises as to how the two can respond so differently to the 

 same influence, and to determine this we need first to find out 

 whether the position taken by the side roots is in any way 

 correlated with that of the main root or is independent of it. 



82. Is there any correlation of position between the main and 

 the side roots? 



Answer by Experiment 48. 



EXPERIMENT 48. To answer this it is only needful to remove 

 the tip of the main root, and observe whether the side roots remain 

 unaffected. After the growing roots in Experiment 44 show r small 

 side roots, mark their positions upon the glass with waterproof 

 India ink. Cautiously slip the glass up in its groove until the main 

 root-tip is exposed ; cut this squarely and cleanly off 5 mm. behind 

 its end, and replace the glass ; observe effects upon the growth of 

 the nearest side roots. 



If Experiment 44 has been tried with the moist-chamber instead of the 

 germination-box, the tips of the roots may easily be removed, though 

 the subsequent growth of the side roots cannot be so accurately deter- 

 mined as with the germination-box where their course may be marked 

 upon the glass. 



83. In what part of the root does the geotropic response nor- 

 mally take place ? 



Answer by Experiment 49. 



