IRRITABLE RESPONSE 



221 



jar with water on the bottom, and a water-filled porous saucer for a top, 

 the seeds being supported on corks and a tumbler, and kept wet by cotton 

 wicking, as shown by the figure. The plants may be swung through 45 

 and 90 by loosening the pins and resetting them in the new position. The 

 whole arrangement is enclosed by 

 a suitable removable hood, and 

 aeration is provided by a daily 

 blowing out. In this chamber 

 the seeds germinate well-nigh 

 ideally and show well the posi- 

 tions taken by the new parts. In 

 such chambers the seeds may be 

 supported simply by pins holding 

 them to a cork, with interposed 

 cotton wicking, as in figure 59, 

 or may be inserted between folds 

 of wet filter-paper held by rubber 

 bands against a bar of wood, as 

 recommended by REED, or in a 

 cage made of wire netting (dipped 

 in melted hard paraffin to make 

 the metal innocuous), filled with 

 moist sphagnum, as I have used 

 with success. 



DEMONSTRATION METHODS. FlG " 59--GLASS MOIST-CHAMBER FOR STUDY 

 The use of the glass-and-felt-paper OF GEOTROPISM ; X*. 



Chamber above mentioned, using The dark cover is omitted. Further explanation 



in text. 



Corn, Oats, or Barley seeds, gives 



the best, and a well-nigh ideal, simple demonstration for elementary pur- 

 poses, especially as it so easily allows of change of position of the roots and 

 stems. Of course much can be shown as to stems by simply laying potted 

 plants upon their sides, when a very marked response occurs in a few 

 hours. Plants completely inverted give striking results. 



The results of the foregoing experiment leave no doubt that 

 growing parts assume an up-and-down position quite regard- 

 less of the positions of the parts from which they start. The 

 sole determinant of up and down, under the conditions of the 

 experiment, is gravitation, which, therefore, would seem to be 

 the guiding influence. This raises an interesting correlative 

 problem as follows: 



What effect is produced upon young growing parts i} gravi- 

 tation is not allowed to influence them? 



Obviously it is not possible to remove any object from the influence 

 of gravitation, but it is possible to use a substitute method, viz., one 



