84 HISTORY OF BOTANY 



bendings. " As gravitation could produce these effects/* 

 he says, " only while the seed remained at rest and in the 

 same position relative to the attraction of the earth, 

 I imagined that its operation would become suspended 

 by constant and rapid change of the position of the 

 germinating seed, and that it might be counteracted by 

 the agency of centrifugal force." He then attempted to 

 prove his theory experimentally by placing germinating 

 seeds on the circumference of a wheel which was made 

 to revolve with great rapidity in a vertical plane. " The 

 radicles of these seeds," he continues, " were made to 

 point in every direction, some towards the centre of the 

 wheel and others in the opposite direction ; others as 

 tangents to its curve, some pointing backwards and 

 others forwards, relative to its motion ; and others 

 pointing in opposite directions in lines parallel with the 

 axis of the wheel. I had soon the pleasure to see that 

 the radicles in whatever direction they were protruded 

 from the position of the seed, turned their points out- 

 wards from the circumference of the wheel, and in their 

 subsequent growth receded nearly at right angles from 

 its axis. The germens on the contrary took the opposite 

 direction, and in a few days their points all met in the 

 centre of the wheel." 



Knight then altered the position of his wheel so as to 

 make it revolve in a horizontal plane at different rates, 

 trying in this way to find what would be the result of 

 combining gravity with centrifugal force. " The difference 

 I had anticipated between the effects of rapid vertical 

 and horizontal motion soon became sufficiently obvious. 

 The radicles pointed downwards about io° below, and 

 the germens as many degrees above, the horizontal hue 

 of the wheel's motion ; centrifugal force having made 

 both to deviate 80° from the perpendicular direction 

 each would have taken, had it vegetated at rest. 

 Gradually diminishing the rapidity of the motion of the 

 horizontal wheel, the radicles descended more perpen- 



