96 REPRODUCTION OF PLANTS. 



be thrown off when a rapid rotatory motion was 

 given to the wheels. One wheel was disposed 

 horizontally, the other vertically, and both were 

 kept in constant motion while the beans were 

 germinating. The radicles of those beans which 

 germinated on the vertical wheel extended them- 

 selves outwards, or from the centre, and the 

 plumules inwards, or towards it. Those which 

 were placed on the horizontal wheel pushed 

 their radicles downwards and their plumules up- 

 wards ; but the former were also inclined from 

 and the latter towards the axis of the wheel. 

 This inclination was found to be greater as the 

 velocity of the wheel was increased. Now in 

 the vertical wheel the effects of gravity were 

 nullified ; since the beans were constantly chang- 

 ing their position with respect to those parts 

 which were alternately uppermost and lower- 

 most, in each revolution. The only cause which 

 could have produced the effects described must 

 be the centrifugal force, which has here replaced 

 the effects of gravity, compelling the root to grow 

 outwards and the stem inwards, instead of down- 

 wards and upwards. The effect produced upon 

 the horizontal wheel is evidently the result of 

 the combined action of the forces gravity in- 

 clining the root downwards, and the centrifugal 



