Chap. IV.] THE EFFECTS OF HEAT. 61 



the cells of the twisted portions was aggregated into distinct though 

 excessively minute purple spheres. This case shows clearly that the 

 protoplasm, after having been exposed to a high temperature for a 

 few minutes, is capable of aggregation when afterwards subjected 

 to the action of carbonate of ammonia, unless the heat has been suffi- 

 cient to cause coagulation. 



Concluding Remarks. As the hair-like tentacles are ex- 

 tremely thin and have delicate walls, and as the leaves were 

 waved about for some minutes close to the bulb of the 

 thermometer, it seems scarcely possible that they should not 

 have been raised very nearly to the temperature which the 

 instrument indicated. From the eleven last observations we 

 see that a temperature of 130 (54,4 Cent.) never causes 

 the immediate inflection of the tentacles, though a tem- 

 perature from 120 to 125 (48.8 to 51.6 Cent.) quickly 

 produces this effect. But the leaves are paralysed only for a 

 time by a temperature of 130, as afterwards, whether left in 

 simple water or in a solution of carbonate of ammonia, they 

 become inflected and their protoplasm undergoes aggregation. 

 This great difference in the effects of a higher and lower tem- 

 perature may be compared with that from immersion in 

 strong and weak solutions of the salts of ammonia; for the 

 former do not excite movement, whereas the latter act ener- 

 getically. A temporary suspension of the power of move- 

 ment due to heat is called by Sachs* heat 'rigidity; and this 

 in the case of the sensitive plant (Mimosa) is induced by its 

 exposure for a few minutes to humid air, raised to 120 

 122 Fahr., or 49 to 50 Cent. It deserves notice that the 

 leaves of Drosera, after being immersed in water at 130 

 Fahr., are excited into movement by a solution of the carbon- 

 ate so strong that it would paralyze ordinary leaves and 

 cause no inflection. 



The exposure of the leaves for a few minutes even to a 

 temperature of 145 Fahr. (62.7 Cent.) does not always 

 kill them; as, when afterwards left in cold water, or in a 

 strong solution of carbonate of ammonia, they generally, 

 though not always, become inflected; and the protoplasm 

 within their cells undergoes aggregation, though the spheres 

 thus formed are extremely small, with many of the cells 

 partly filled with brownish muddy matter. In two instances, 



* Tralte de Bot.' 1874, p. 1034. 



