GEOTROP1SM. 



123 



given by Darwin and Acton, and in principle has been used in recent 

 researches by F. G. Kohl (Botanische Zeitnng, 58, i). 



FIG. 33. SIMPLE ARRANGEMENTS FOR STUDY OF GEOTROPIC BENDING. 



One-third the true size. 



86. What effect is produced upon the growth-processes when 

 geotropic stimuli are allowed to act but growth-response is pre- 

 vented ? 



Answer partly from Experiment 50, and from Experiment 



EXPERIMENT 51. This may be tested by placing a positively or 

 negatively geotropic growing part, such as a shoot, horizontal, pre- 

 venting it from bending geotropically and later suddenly releasing 

 it. Invent a way of accomplishing this. 



87. Is the geotropic response simply mechanical and passive, 

 or can it take place against resistance? 



Answer by Experiment 52. 



EXPERIMENT 52. This may be tested by placing a geotropically- 

 growing part, such as a root, in such a position that, in order to 

 continue its growth downwards, it must exert a distinct, and prefer- 

 ably measurable, pressure. Such a resistance-measurer in which 

 the flotation-power of mercury is utilized is shown in Fig. 34 on the 

 left. Select a large upright perfectly clean test-tube, and a vial 

 (which is lighter than glass tubing of the same diameter) somewhat 

 smaller in diameter than the tube. Remove (by the method de- 



