142 



PHYSIOLOGY OF NUTRITION. 



of the wooden base is screwed the wooden socket supporting a 

 glass cylinder, g, 10 cm. high and 35 mm. in diameter. This 

 cylinder receives the seeds and water. It is made water-tight 

 at the bottom by means of sealing-wax. In the cylinder moves 

 loosely a metallic piston, s, supported by a vertical piston rod, a, 

 16 cm. in length. The piston rests immediately on the seeds. 

 The cylinder is closed by the metallic cap &, through the middle 

 of which passes the piston rod, so that the cap can be freely 

 twisted round it. The piston rod carries at the top a brass disc, 



FIG. 49. Apparatus for measuring the external work performed by swelling seeds 



s', intended to support a weight. Between the cap k and the 

 disc s' the horizontal lever z is attached to the piston rod by 

 means of a screw, so that it can be fixed at different heights. 

 Its fulcrum is at u. The short arm of the lever is 2 cm. long, 

 the long arm about 33 cm. long. The pointer reaches to the 

 circular arc s~k (represented on the right-hand side in the illus- 

 tration), which is graduated in centimetres. Any upward move- 

 ment of the piston, due to the pressure exerted by the swelling 

 seeds, effects a downward movement of the pointer, which renders 

 it possible to ascertain on a correspondingly magnified scale the 

 movement of the piston resulting from the swelling of the seeds. 

 10 gr. of small peas placed in the apparatus were able to over- 

 come a resistance of 1,000 gr. 



1 Literature': Sachs, Handbuch d. Experimentalphysiologie d. Pflanzen, 1865, 

 p. 431 ; Detmer, VergL Physiologic d. Keimungsprocesses d. Samen, 1880, pp. 

 78 and 290 ; Eeinke in Hanstein's Botanische Abhandlungen, Bd. 4, H. 1 ; 

 Schleicbert, Naturwissenschl. Wochenschrift, Bd. 7. 



