No. 507] BOTANICAL SOCIETY OF AMERICA 



157 



other matters lie has amply shown that he was not afraid 

 to combat what to him were mere conventionalities. 



A large portion of his book on climbing plants is 

 devoted to a consideration of the tendril bearers and 

 takes up a wide range of forms. The exceeding sensitive- 

 ness of these organs to contact Darwin was one of the 

 first to appreciate, but he went somewhat astray in sup- 

 posing that mere pressure was enough to induce the 

 characteristic coiling response. It was not thoroughly 

 understood until later that weight alone is not sufficient, 

 but that the stimulus must involve some more intricate 

 contact shock. He did not understand that the exciting 

 body must have a certain degree of what one may call 

 roughness and consequently he did not understand the 

 inaction of tendrils to raindrops. 



His conclusions did not wholly agree with the now 

 accepted explanations of the nature of the response of 

 tendrils but it inclined to the view that the rapid reply of 

 incurving tendrils was primarily caused by turgor 

 changes ultimately rendered permanent by growth. More 

 recently it has again been claimed that the curvature is 

 wholly a growth phenomenon, but in so much as turgor 

 changes are often apparently so greatly concerned with 

 the first stages of cell enlargement incident upon growth, 

 may not the initial curvature be after all a matter of 

 unequal turgor pressure on the two sides of the tendril* 

 Here as in other places Darwin considered the response 

 of contact stimulus a form of modified nutation. 



Although Drosera and similar plants were not con- 

 sidered by Darwin in this connection, in so much as some 

 phases of his study had to do with their response to con- 

 tact irritation, it is suitable to introduce the matter now. 

 His investigation of the behavior of Drosera was espe- 

 cially detailed and represented at the time a great ad- 

 vance in the knowledge of the habits of this insectivorous 

 form. There is not, as a matter of fact, any more elabo- 

 rate or complete study at present, although his results 

 were published some thirty years ago. Many important 



