Behavior of Stigma Lips. 267 



sisting of curvature, is confined to the stimulated zone. There 

 appears therefore no evidence that the stimulus is transmitted 

 either from one lip to the other (as occurs according to Oliver, 

 /. c, in Marlynia and in Mimulus cardinalis, but not in Mim- 

 ulus luteus) or within the sensitive areas of either lip. That there 

 is a slow transmission if possible, but such has not been observed 

 in the course of the work. Mimulus lateus appears to me to be 

 in the same case. 



There appears to be no cumulative eflfect of mechanical 

 stimuli of slight amount, each ineffective in itself. 



Mechanical stimulation of the papillae of the stigmatic sur- 

 face sufficient to bend these, but not the lip, is non-eflfective. 

 "Touch" is not a stimulus and the stigmatic papillae are not 

 sense organs. 



The piesence of pollen does not prevent a reopening of the 

 stigma-lips, when these are closed at the time of pollination by 

 mechanical stimulus. Whether so closed or not, the pollen 

 causes closure beginning in about three or four hours, by the 

 withdrawal of water from the underlying tissues. According to 

 the position of the pollen this closure may be complete and in- 

 Volve both the lips, or partial, consisting of more or less pro- 

 nounced curvatures in one or the other lip. This conclusion is 

 in general agreement with that of Burck cited above, with whose 

 observations on the effect of pollen in preventing the reopening 

 of the stigma-lips my own on Z)i/'/actw are in disagreement. The 

 closure due to pollen is not an irritable response, but is analog- 

 ous to that induced bv heat or alcohol and its vapor, in that it 

 is accompanied by partial or entire disorganization of the tissues. 

 The position of the stigma-lips, under such conditions, is to be 

 referred to the physical properties of the thick outer wall of the 

 epidermis of their outer faces, and not to turgor differences 

 within the motile tissues. 



A comparison of the conditiofis in Dionaea and in Diplacus, 

 suggests the view that mechanical stimulus is made eft'ective 

 through a stretching of the sensitive cells, either local or involv- . 

 ing the entire cell. 



Alabama Polytechnic Institute 

 Auhtirn, Alabama. 



