120 PLANT PHYSIOLOGY. 



be kept from acting unilaterally upon an object is by making it equal- 

 ize itself by a constant and uniform revolution of the object in a ver- 

 tical plane. Select two good corks some 12 cm. in diameter, and pin 

 to each, in as different positions as possible, some five good soaked 

 horse-beans, bringing the latter away from the cork to the heads of 

 the pins. Surround and cover both with moist chopped sphagnum, 

 and over each cork place a crystalliziug-dish about 6 cm. deep, of a 

 size proper to hold tightly when pressed over the bevelled edge of 

 the cork. Attach one of the corks to the disk or arm of a clinostat, 

 and keep it revolving in a vertical plane once in fifteen minutes 

 (to allow a complete revolution within the reaction-time of the roots), 

 and set the other in a fixed vertical position (see Fig. 32). Compare 

 from day to day the positions taken by the roots on the two corks. 



FIG. 32. A SIMPLE CLINOSTAT. 

 One-third the true size. 



A clinostat is necessary for this as for other physiological work, and 

 is simply indispensable for any physiological laboratory. That most used 

 is Wortmann's, costing about $60, which may be imported through any 

 dealer in scientific apparatus. A more expensive one is Pfeffer's, made 

 by Albrecht, costing about $100, while one recently described by Hansen 

 (in Flora, 84, 353) is advertised at 115 marks ($29). A simple form run 

 by a water motor is described by Stevens (Botanical Gazette, 20, 92), and 

 another run by clockwork by Stone (Botanical Gazette 22, 259). A 

 comparatively inexpensive and, for purposes of investigation of the 

 principle of geotropism, heliotropism, etc., entirely efficient clinostat may 

 be made as follows (see Fig. 32): Procure a Seth Thomas eight-day clock 

 (costing about $6), and have a watchmaker remove hands, face, and 

 surplus works, and gear it down so that the minute-hand spindle turns 



