BthAViok OF StiGMA Lips. 265 



in a vessel of vater to which heat was applied from below. A 

 thermometer was introduced from above, the bulb being placed 

 near the stigma of a flower standing in water in a vial. The 

 corolla was removed sufficiently to expose the stigmas. Other 

 experiments were done as indicated bebw. 



If an open stigma is placed carefully in hot (nearly boiling) 

 vvater the lips close on being killed. The same is true if the 

 lips are held with their stigmatic faces near the surface of the 

 hot water. When killed the tissues become opaque and yellow- 

 ish in color. This closure is h )wever preceded by a slight curl- 

 ing back of the lips, a movement which is probably caused by 

 the expansion of the water in the cells just previous to its 

 escape through the protoplasm. There appears to be no clos- 

 ing response to heat below the thermal death point. This was 

 indicated in the follo\\ing manner. Three stigmas, attached 

 to the flo\. eis, from which for convenience the upper part of the 

 corollas had been removed, were held near a hot water surface, 

 until the slight curling back was noticed. Two of these were 

 killed by the exposure. The third survived, remaining open, 

 in which positi'^n it was found the following morning. The 

 edges of the lips had been killed however, and w^ere withered. 



The thermal death point was determined by exposure of 

 the preparation to heat in the apparatus above described. A 

 series of trials showed that the point lies very near to 58 degrees 

 C. Thus an exposure for one minute to temperatures beginning 

 with 58.5, falling to 57.5 and rising to 58.3 resulted in killing 

 the stigmas but not the limb of the corolla, which had not been 

 removed. Similar exposure with a range of temperatures of 

 59, falling to 58 and rising to 58.3 killed both the stigmas and 

 corolla. One minute at 57, or a small fraction of a degree 

 above and below did not kill. At the conclusion of the trials, 

 the remo\al of the bell-jar caused air-currents which were 

 sufficient to cause in some cases the closing of the lips. That 

 this was due to the mechanical disturbance and not the heat 

 was shown by the result that, with very careful manipulation, 

 so as to avoid an inrush of air, closure did not ensue. Thus, 

 after a four minute exposure to 45 to 41 degrees and to 44 to 

 43 degrees, there was no response, nor after a one minute ex- 



