266 The Plant World. 



posure to 48 to 47 degrees, when removal of the bell- 

 jar was carefully accomplished. In one instance however, 

 the evidence was not unequivocal, and there was observed 

 some straightening of the lip, even before the removal of the 

 bell-jar after one minute exposure to 50 to 51 degrees. The 

 positive evidence obtained appears however to point to another 

 explanation rather than to a true response. 



The behavior toward alcohol and its vapor is analogous 

 to that toward heat. When gently placed in nearly boiling 

 absolute alcohol, the lips close instantly. In cold absolute 

 alcohol closure occurs more slowly, beginning in 20 seconds and 

 being completed in about 50 to 60 seconds. In cold alcohol, 

 however, there is a slight backward curling previous to clo„uie 

 which may perhaps be referred to the shrinkage of the thick 

 epidermis of the outer surface of the lip. The closing move- 

 ment is of the same character ^\ hether induced by heat or alcohol, 

 and ends when the lips have straightened. 



Exposure to alcohol vapor under a glass for 28 minutes 

 caused closure from which there was no recovery, the tissues 

 being evidently dead, as three hours later they had quite shriv- 

 elled. There was no movement after 15 minutes exposare (ap- 

 proximately the maximum non-lethal dosage) but the lips 

 closed on being stimulated mechanically. They subsequentlv 

 opened, showing that no permanent deleterious effect of the 

 alcohol was had. Alcohol, therefore, unlike ammonia gas (ac- 

 cording to Correns) does not act as a stimulant but, like hydro- 

 cliloric acid vapor, (Correns) and heat causes closure only by 

 killing. It seems probable that anaesthetization by alcohol 

 cannot be accomplished without injury. 



CONCLUSIONS 



The closing response of the stigma-lobes in Diplacus is eff- 

 ected by mechanical displacement , only if of sufificient rapidity 

 and when applied against the stigmatic surface. When the sti- 

 mulus is applied against the outer, non-papillate face of the lip 

 it is non-effective. The case is thus analogous to that of the sen- 

 sitive trichomes in Dionaea (Brown and Sharp, /. c). 



If mechanical stimulus is applied so as to bend only the 

 cells within a particular zone of the stigma-lip, the response, con- 



