CH. VII] KLINOSTAT. 189 



end of a bit of lead wire, of which the other end rests on 

 the board b. If this precaution is neglected the loop of 

 silk may become entangled in the clock wheels, or the clock 

 may be forcibly stopped by touching one of the wheels in 

 such a way that the escapement becomes fixed ; and this 

 never happens if the balance-wheel is stopped as above 

 described. If proper care is taken a box of earth and 

 plant weighing together 1000 grams may easily be kept 

 in constant rotation. If the apparatus seems at all top- 

 heavy a heavy weight wt, fig. 36, may be placed on the 

 board. 



For experiments on diaheliotropism Ranunculus ficaria 

 is useful, as it is obtainable early in the year and grows 

 healthily indoors. We cultivate Ficaria by wrapping the 

 roots in wet cotton-wool protected by a covering of india- 

 rubber cloth. The plants so treated are fixed by means 

 of large pins to a cork disc taking the place of the box B 

 in fig. 36. The klinostat is placed as close as possible to 

 the window, and it is desirable, though not necessary, to 

 keep extraneous light away by a black curtain hung 

 behind and at the sides of the apparatus. 



The following fundamental experiments should be 

 performed 1 . 



(i) When a Ficaria plant is dug up, its leaves freed 

 from the resistance of the soil, curve (epinastically) strongly 

 downwards. If such a plant is fixed with its axis horizontal 

 and parallel to the spindle of the klinostat, and if the 



1 See F. Darwin, loc. cit.; also Yochting, Bot. Zeitnng, 1888; Krabbe, 

 Pringsheim's Jahrbucher, Vol. xx.; Schwendener and Krabbe, A". Preuss. 

 Akad. Abhand. 1892. 



