LEAVES WITH REGABD TO LIGHT. 425 



been fully discussed by Sachs in his paper, " Ueber Ausschliessung 

 der geotropischen und heliotropischen Kriimmungen " *. The 

 history of the subject is there given; and a quotation from Sachs's 



• Experimental Physiologie ' (1865) shows that the principle of 

 slow rotation was fully understood by him at that time. He 

 points out (p. 107 f) "that before any curvature, and before a 

 perceptible amount of growth could occur" .... the plant 

 " would be in a reversed position." Thus any tendency to cur- 

 vature which had been generated in the first position would be 

 destroyed in the second position, and the plant would have no 

 geotropic tendency of any kind. 



Sachs is acquainted with John Hunter's experiments only as 

 quoted by Dutrochet, and has not been able to see the original 

 paper. And as Dutrochet quite misrepresents Hunter's meaning, 

 it may be worth while to show that Hunter had a clear concep- 

 tion of the principle of slow rotation. He describes the means 

 by which a basket of earth containing germinating beans was 

 made to rotate, and goes on to say that the root of a bean had 

 met with a small stone in its course, and had been turned by it 

 into the direction of the axis of rotation, and had then (/one on in 

 a straight line in that direction. " Here, as there was no fixed 

 inducement to grow in any one direction, the bean grew in a 

 straight line in that direction given it by chance "J. 



The above quotation has a merely antiquarian interest, the 

 method of slow rotation as it exists in modern physiological 

 research, and especially the ingenious application of it to the 

 study of heliotropism, is entirely due to Sachs. 



In describing the application of the principle of slow rotation 

 to the study of plagiotropic organs, I shall employ Sachs's term 

 Klinostat to designate the instrument by which plants are kept 

 in slow rotation. And I shall employ this term to signify an 

 apparatus either for the avoidance of geotropism alone, or of 

 both heliotropism and geotropism § . 



Fundamental Experiment— If a plant whose leaves have the 



* Arbeiten, Wurzburg, Bd. ii. Heft ii. p. 209. 

 t Quoted by Sachs in his Arbeiten. 



| Quoted from Hunter ' On the Blood ' (1794), in the Catalogue of the 

 Physiological Series of Comparative Anatomy in the Museum of the Boy. Coll. 

 of Surgeons, toI. t. 1840, p. 12. 



§ For the detailed description of the klinostat used in my experiments see 

 Appendix. 



