66 THE METHOD OF DARWIN. 



beans at a temperature of 69-72 F. The 

 result was moderately distinct deflection in only 

 one radicle; in five other cases slight and 

 doubtful deflection. "We were astonished at 

 this result, and concluded that we had made 

 some inexplicable mistake in the first six experi- 

 ments. But before finally relinquishing the 

 subject, we resolved to make one other trial, 

 for it occurred to us that sensitiveness is easily 

 affected by external conditions, and that radi- 

 cles growing naturally in the earth in the early 

 spring would not be subjected to a temperature 

 nearly so high as 70 F." In the vast num- 

 ber of successful trials that they made they 

 allowed the radicles to grow at a temperature 

 of 55-6o F. 1 



Had they stopped with the first trial, they 

 would have hit the explanation which they 

 finally adopted, and missed the effect of varia- 

 tions in temperature. Had they stopped with 

 the second, the question would have hung in 

 the balance between contradictory results. It 

 was very feasible to reason that the results of 

 the older experiment were due to some error of 

 observation or manipulation. Nothing would 

 have been known concerning the effect of tem- 

 perature, and nothing concerning the original 



1 Power of Movement in Plants, pp. 141, 142. 



