EXHAUSTIVENESS. 6/ 



question. Their imagination had led them to 

 introduce a new element into the second experi- 

 ment; then reason prevented them from suc- 

 cumbing before the disturbance in the results, 

 and led them to recognize it as a determining 

 factor and treat it as such in their subsequent 

 experiments. 



The contradictory state in which things would 

 have been left at the end of their second experi- 

 ment is neatly illustrated by another case in 

 connection with the same subject. 1 Ciesielski 

 had shown, in his study of geotropic move- 

 ments, that roots extending horizontally with 

 their tips cut off did not grow downward. " He 

 further states that, if the tips are cut off after 

 the roots have been left extended horizontally 

 for some little time, but before they have begun 

 to bend downwards, they may be placed in any 

 position and yet will bend as if still acted on 

 by geotropism ; and this shows that some influ- 

 ence had been already transmitted to the bend- 

 ing part from the tip before it was amputated." 

 Sachs repeated these experiments, but denied 

 the conclusions, because in his experiments 

 the roots became distorted in all directions. 

 The Darwins undertook to learn the cause of 

 the contradiction in the results. After describ- 



1 Power of Movement in Plants, p. 523. 



