456 PHYSIOLOGY OF GROWTH. 



so fixed in the support that the weight is in excess on one side of 

 the axis of rotation, then a particular side of the pot will 

 always be found at the bottom when the apparatus conies to rest, 

 the centre of gravity lying below the axis of rotation. By now 

 fixing the centering arrangement on the opposite side of the shaft, 

 and adjusting the position of the weight on the pin, the effect of 

 the inequality may after a few trials be eliminated, so that the 

 pot will come to rest in any position after rotation. When the 

 centering has been accurately performed, the shaft / is put in 

 connection with the clockwork. This is effected as follows by 

 simply pushing in the knob d of Fig. 148. 



Each of the three spindles a, b, and c carries a toothed wheel, 

 as indicated by Fig. 149, which represents a longitudinal section 

 through the clockwork. The toothed wheels of the spindles 7) 

 and c engage with one another always; that of the spindle a 

 does not directly engage with them. By pushing home a wheel, 

 '^, shaded in the drawing, whose teeth gear into the wheels of 

 the two upper spindles, and also into one wheel of the clockwork, 

 all three spindles are set in motion simultaneously. Fig. 150, 

 which represents another longitudinal section through the clock- 

 work in a direction at right angles to that of 149, shows clearly 

 how the connecting wheel q is operated. 



In the figure there is no connection between the clockwork and 

 the spindles, the connecting wheel q not being in gear. By 

 pressing on the knob p, the connecting wheel is pushed home, 

 and by sliding down the knob p', it is held in place. If any 

 operation has to be performed on the research material while the 

 rotation is proceeding, if, for example, it is desired to water the 

 soil in the pot and so forth, the communication between clock- 

 work and shaft must always be first broken by drawing out the 

 pin p. 



To effect rotation about a horizontal or inclined axis, but with 

 the rotating object disposed in a direction at right angles to that 

 indicated in Fig. 148, we fix the flower-pot by means of wire into 

 one of the three rings represented in Fig. 151. For inclined axis 

 of rotation the friction rollers are fixed on a second very strong 

 stand. 



If we are concerned with observations on objects requiring 

 to be kept in a moist space, such as say fungi (sporophores of 

 Phycomyces), roots, disconnected plant structures, etc., we may 

 fix them on a brass axis 80 cm. long (not represented in the figures) 



