80 RELATION OF PLANTS TO GRAVITATION 



for a short time even after the stem had been brought to a 

 complete rest, and placed in an upright position. 1 Similar re- 

 sults have been obtained with phototropic stimuli by Czapek 

 and Wiesner. 



120. Rhythmic Effects of Alternating Stimulation. Select a 

 small vigorously growing shoot of some convenient plant such 

 as Helianthus. Cut off the tip under water and pass the base of 

 the excised part through the cork of a bottle filled with water. 

 Fix a fiber or small needle to the tip in a position exactly parallel 

 to the axis of the shoot. The shoot must be about 12 to 20 

 cm. in length. Place the bottle on its side with the shoot in a 

 horizontal position. Set a finely divided scale in a perpendicular 

 position to one side of the needle, or fiber index. As soon as the 

 index begins to travel upward, showing that the shoot is curving 

 apogeotropically, revolve the bottle half way round on its axis. 

 Note the position of the point and follow its movements for an 

 hour or two. Observe again to 14 hours later. 



121. Chemical Changes in a Geotropically Stimulated Root. 

 Place a number of seedlings of Vicia Faba in a damp chamber 

 for an hour with the roots horizontal, and others with the roots 

 directed normally downward. An hour later select one root of 

 each lot and quickly slice into four longitudinal sections. Lay 

 the sections in watch crystals containing an emulsion of guiacum 

 in ten-per-cent. alcohol, which has been prepared some time be- 

 fore. The sections from the unstimulated root are seen to take a 

 darker blue color than the others. 



Crush a number of stimulated and unstimulated roots in sepa- 

 rate watch glasses full of salt solution consisting of I g. sodium 

 chloride in i ooo cc. of water. Add a few drops of sodium hydrate 

 and set aside for an hour. The preparation from the unstimulated 

 organs will show a darker brown color than the other. The lack 

 of color in the first and its presence in the second, is taken by 

 Czapek to be due to the presence of an oxidizing ferment in the 



1 Darwin and Pertz. On the artificial production of rhythm in plants. Annals of 

 Botany, 6 : 245. 1892. 



