Page:Insectivorous Plants, Darwin, 1899.djvu/81

 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 sufficient to cause coagulation. Concluding Remarks.―As the hair-like tentacles are extremely 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 temperature 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 temperature 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 energetically. A temporary suspension of the power of movement 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 carbonate 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,