ISOLATED PHENOMENA. 57 



tions of the universal movement of circumnu- 

 tation. In his experiments on insectivorous 

 plants with phosphate of ammonia he varied 

 the proportion of the latter to determine how 

 small an amount would affect the tentacles of 

 Drosera. 1 He found that excessively minute 

 quantities of the latter would produce reac- 

 tion. His results were so astonishing that in 

 1873 he doubted his own experiments of 1872, 

 and in 1874 he again thought that some mis- 

 take must have been made, and again repeated 

 the experiments, but always with the same 

 results. He discussed these remarkable facts 

 at some length, tried to make them more cred- 

 ible by comparing them with similar cases that 

 are equally astonishing but are known to be 

 true; and expressed the hope that his experi- 

 ments would be repeated, at the same time 

 laying down the conditions of success. 



While studying the power of circumnutation 

 in plants the Darwins accidentally left some 

 of their specimens in several cases exposed to 

 oblique light. Before they "knew how greatly 

 ordinary circumnutation was modified by a 

 lateral light, some seedling oats, with rather 

 old and therefore not highly sensitive cotyle- 

 dons, were placed in front of a northwest win- 



1 Insectivorous Plants, pp. 154-173., 



