GEOTROPISM. 127 



geotropic, and the question arises as to what extent other 

 organs are. 



89. Do flowers show geotropism '? 



Answer by Experiment 53. 



EXPERIMENT 53. This may be answered by observation of the 

 behavior of young flowers in clusters made to develop in other than 

 their natural position. Select a small plant with a developing cluster 

 of (preferably zygomorphic) flowers, such as a potted Delphinium. 

 Carefully bend over the stalk of the cluster and tie the latter as 

 nearly upside down as possible ; set it in darkness to make sure the 

 resultant is not simply a light effect, and observe results. 



90. Are leaves geotropic? 



Answer by Experiment 54. 



EXPERIMENT 54. Take a Tropaeolum plant, and tie its stem to a stick 

 so it cannot materially alter its position ; place the pot on its side 

 in entire darkness for twenty-four hours, and note the positions 

 taken by the leaf-blades. Most other plants will behave similarly ; 

 try one with a pulvinus, such as a developing bean, and a " stemless ' 

 plant like an Oxalis. 



91. What ecological phases of geotropism can you trace? 



There is much simple and beautiful experimentation practicable upon 

 dia-, lateral, and transverse geotropism, though time hardly admits of 

 their further investigation here. The diageotropism of roots may be 

 most beautifully illustrated by placing seeds upon the flat ends of the 

 germinators used in the hydrotropism experiments (Experiment 58, 

 Fig. 35). Also, it comes out clearly in seeds grown in the germination- 

 boxes (Fig. 30). It is most instructive when, after the roots are of good 

 size, the glass or other surface against which they grow is turned in the 

 same plane through 45. Very important ecologically, and easy to study, 

 is the lateral geotropism of the stems of twining plants. To thoroughly 

 test this, the plant should be placed with its support at various angles 

 between the vertical and horizontal, and the critical angle below which 

 it will not twine determined. The transverse geotropism of many root- 

 stocks and trailing plants is to be noted. 



92. In a paragraph express your idea, derived from con- 

 sideration of all of your sources of information, of the exact 

 nature of Geotropism, including (a) the factors concerned in 

 the process, (7?) its use to the plant, and (c] the reason why it 

 is so extensively used. 



