20 RELATIONS OF PLANTS TO MECHANICAL FORCES 



ceae. Portions of the style or stigma are sensitive in Martynia, 

 and Mimulus. * 



27. Accommodation of Mimosa to Repeated Mechanical Shock. 

 Place a well-grown specimen upon a drained bench in a green- 

 house in strong light and a temperature of 25 to 30 C. Fasten 

 a sheet of rubber cloth around the base of the stem in such man- 

 ner that water falling upon the plant will not reach the soil in the 

 pot. Set a tub or cask on a support a meter or two above the 

 plant and arrange a connection with a water system that will keep 

 it full. The water in the cask will thus acquire the approximate 

 temperature of the air. Arrange a siphon tube with a spray 

 nozzle so that a constant spray will fall on the leaves of the plant 

 in such manner as to resemble a shower of rain. If a system of 

 warm water is at hand the spray may be given directly from the 

 pipes, but care must be taken to secure the proper temperature 

 as above. Note the behavior of the leaves when the shower be- 

 gins. Observe the plant at intervals throughout the day, and de- 

 termine the time necessary for it to emerge from the state of 

 tetanus into which it is thrown by the repeated stimulation of the 

 falling drops of water. On the following day, after the leaves 



FIG. 8. Nozzle suitable for spraying Mimosa. 



have resumed their accustomed position and have become accus- 

 tomed to the repetition of the stimulus, send a sudden gust of air 

 against the leaves. This mechanical stimulus of a different in- 

 tensity and direction will cause closure of the pinnules and other 



1 Hansgirg, A. Ueber die Verbreitung der Reizbaren Staubfaden und Narben, 

 sowie der sich periodisch oder bios einmal offenden und schliessenden Bluten. 

 Bot. Centralblatt. 43 : 409. 1890. 



