176 KLINOSTAT. [CH. VII 



(219) Mode of action of the klinostat. 



Two views are possible as to the mode of action of the 

 klinostat. It might be supposed that the plant does not 

 curve geotropically (or heliotropically as the case may be) 

 because it never has time to perceive the stimuli. Or, it 

 might be supposed that the stimulus is perceived but 

 is equally distributed. An experiment of Elfving's^ shows 

 that in some cases at least the latter is the explanation. 

 If a grass-haulm which has finished growing is kept in a 

 vertical position, the pulvinus undergoes no change, but 

 growth does take place in the pulvinus of a grass-haulm 

 kept in slow rotation on the klinostat. This seems 

 to prove that just as the gravitation-stimulus acting on a 

 horizontal stationary pulvinus produces one-sided growth, 

 so an equally distributed stimulus produces a symmetrical 

 growth, i.e. a simple increase in length of the pulvinus. 

 The pulvini must be marked, and measured microscopically, 

 and they may then be fixed inside a large corked test-tube 

 and kept in rotation for 3 or 4 days. If the test-tube 

 contains a little water the haulms will be kept sufficiently 

 damp. As a control similar haulms must be placed 

 vertically in a stationary test-tube. This precaution is 

 necessary because the pulvini may not have completed 

 their growth so that the control specimens will show 

 a certain amout of elongation. 



(220) The peg or heel of Cucurbita. 



A similar conclusion may be drawn from the 

 behaviour of germinating cucurbits on the klinostat. 



' Ofversigt af Finska vetenskaps Societets FdrJumdlingar, 1884. 



