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Show 72 DROSERA ROTUNDIFOLIA. CHAP. IV. Expm·iment 11.-A leaf was immersed in water at 145° (62° · 7 Cent.), which was raised to 156° (68°·8 Cent_.). The tentacles became bright red and somewhat reflex:ed, WI~h al~ost ~II .the glands like porcelain; th~se on . the disc bmng ~till pinkish, those near the margin quite white. The leaf being placed as usual first in cold water and then in the strong solution, the cells in the tentacles became of a muddy greenish brown, with the protoplasm not aggregated. Ne~ertheless, four ~f the glands escaped being rei;J.dered like porcelain, and the pediCels of the~e glands were spirally curled, like a French horn, to:wards their upper ends; but this can by no means. b~ considered as a case of true inflection. The protoplasm within 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. Prom 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.) qnickly 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 tern porary suspension of the CHAP. IV. THE EFFECTS OF HEAT. 73 power of movement due to heat is called by Sachs* heat-rigidity; and this in the case of the sensitiveplant (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 in to movement by a solution of the carbonate so strong that it would paralyse 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 car.bonate 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, when leaves were immersed in water, at a lower temperature than 130° (54°·4 Cent.), which was then raised to 145° (62°·7 Cent.), they became during the earlier period of immersion inflected, but on being afterwards left in cold water were incapable of re-expansion. Exposure for a few minutes to a temperature of 145° sometimes causes some few of the more sensitive glands to be speckled with the porcelain-like appearance; and on one occasion this occurred at a temperature of 140° (60° Cent.). On another occasion, when a leaf was placed in water at this temperature of only 140°, and left therein till the water cooled, every gland became like porcelain. Exposure for a few minutes to a temperature of 150° (65°·5 Cent.) generally produces this effect, yet many glands retain a * 'Traite de Bot.' 1874, p. 1034. |