CHAP, x The Problems of Growth 457 



claimed to have found that light can play the same part. 

 When he exposed young etiolated seedlings of Phaseolus 

 andCucurbita to light after a period of darkness, the leaves 

 showed epinastic growth. He applied the term photo-epinasty 

 to the phenomenon. Vines investigated the same subject 

 in 1889, and repeated Detmer's experiments, but he failed 

 to confirm his conclusions. Vines denied the existence of 

 photo-epinasty. 



Another discovery of great interest was made by Sachs 

 in 1863, when he found that plants cannot manifest the 

 power of responding to stimulation unless they have 

 been in a favourable position for some time with regard 

 to both light and temperature. He introduced the terms 

 phototonus and thermotonus to express this condition of 

 a plant with reference to these two features of its environ- 

 ment. 



