466 



PHYSIOLOGY OF GROWTH. 



support through an angle of 90, so that its end rests on the metal 

 rod indicated in Fig. 155 by dotted lines, and standing at right 

 angles to the board J3, and then again tightening the set screw 

 Sch. If the plants in the flower-pots are to be removed, during 

 rotation, from the influence of light, we employ sufficiently deep 

 sheet zinc cylinders, pierced near the rim with holes so that they 

 may be fastened to the disc of the apparatus by the screws 

 lettered h, i, A*, in Fig. 156. In use the apparatus is screwed 

 to a bed-plate, which it is best to fix on iron brackets let into 



the wall. 



The screws, as also all the other 

 screws in connection with the 

 apparatus, must be well tightened 

 so that they will not shake loose 

 during the rapid rotation. The 

 apparatus is worked by a water 

 motor (Herbertz, Cologne), to 

 which the necessary water is 

 supplied by means of a tube 

 screwed on the tap of the water 

 supply. The motor is connected 

 with the centrifugal apparatus 

 by means of an endless cord, and 

 a high rate of rotation (four to five revolutions per second) can , 

 easily be attained. 



For examination we first employ cress seedlings grown in well- 

 soaked garden soil. On the disc Msch we lay moist blotting- 

 paper, place a flower-pot on the disc exactly in the middle, fasten 

 it carefully with the supports and at once begin the investigation, 

 which soon leads to the result already indicated above. 



I also experimented, e.g., with young wheat seedlings grown in 

 pots. At a high summer temperature the plumule had already 

 curved towards the centre of the disc after two to three hours' 

 rotation. In experiments on the influence of centrifugal force 

 on the growth of roots, it is best to proceed as follows. The pot 

 supports are removed from the disc, and we place on it a zinc 

 cylinder about 15 cm. long, pierced near the lower end with three 

 holes, so that it can be fixed by means of the screws h, i, and 

 Ic. Just above these holes is the bottom of the cylinder, which 

 therefore rests directly on the disc Much. The upper open end 

 of the cylinder is provided with a cover. The inside of the 



FIG. 156. Disc of the centrifugal 

 apparatus represented in Fig. 155, seen 

 from above. 



