MOVEMENTS OF IRRITATION. 463 



cm. broad, and 41 cm. long. The walls of the smaller com- 

 partment in which the vanes are to move are lined with sheet 

 zinc. In the front is an opening which is closed by means of a 

 perforated cork. Through this passes a glass tube, the end of 

 which towards the varies is somewhat drawn out, while over the 

 other end can be slipped a tube connecting with the water supply. 

 By directing a stream of water on the vanes 200-300 revolutions 

 per minute can be obtained if the force of water is fairly strong. 

 To avoid scattering of the water the smaller compartment is 

 provided with an arched wooden cover. The water dropping 

 from the vanes is carried off by a hole in the bottom of the box 

 direct into the sink on which the apparatus is placed. 



Suitable objects for examination are, e.g., pea seedlings grown 

 in moist sawdust, and provided with roots about 2 cm. long. The 

 cork which rests on the wooden disc H is soaked with water, 

 and on it is placed wet cotton wool. This is fixed by means of 

 pins. We attach the seedlings to the cork, likewise with pins, 

 near its periphery, say with their main roots directed parallel 

 with the axis of rotation. The zinc 

 cover is now coated on the inside 

 with moist blotting-paper and put 

 on. In my investigations at about 

 20 C., the result was already very 

 obvious after three hours' rotation. 

 The growing root tips of the seed- 

 lings fixed to the disc of the appar- 

 atus in various directions had all 

 curved outwards, so that they now 

 formed a right angle with the axis FIG. 154. Seedlings of Pisum, 



f , ,' / -TT,. tt-A\ -r whose root tips, owing to rapid 



of rotation (see Fig. 154). In ex- rota tion of the disc of a centrifugal 



periments lasting for some time, apparatus, have curved about a 

 v i , -i -i , horizontal axis. 



wnicn, e.g., are intended for study- 

 ing the behaviour towards centrifugal force of the secondary 

 roots of seedlings, it is necessary to interrupt the experiments, 

 say every three to four hours, in order to keep the cotton wool 

 on the cork and also the seedlings sufficiently moist by renewed 

 watering. 



The apparatus described is not strong enough to support flower- 

 pots containing soil and seedlings. Bat in order to demonstrate 

 the influence of centrifugal force on growing stems I proceed as 

 follows : - 



