observer[10] has remarked that one variety of the cherry has the petals of its flowers much curled backwards, and after a severe frost all the stigmas were killed; whilst at the same time, in another variety with incurved petals, the stigmas were not in the least injured. [3] This distinction was first pointed out (according to Pfeffer, ‘Die Periodischen Bewegungen der Blattorgane,’ 1875, p. 161) by Dassen in 1837. [4] ‘Flora,’ 1873, p. 433. [5] ‘Bot. Zeitung,’ 1879, Dec. 19th, p. 830. [6] Pfeffer, ‘Die Period. Beweg. der Blattorgane.’ 1875, p. 159. [7] ‘Die Nat. Wagerechte Richtung von Pflanzentheilen,’ 1870, p. 52 [8] Martins in ‘Bull. Soc. Bot. de France,’ tom. xix. 1872. Wells, in his famous ‘Essay on Dew,’ remarks that an exposed thermometer rises as soon as even a fleecy cloud, high in the sky, passes over the zenith. [9] ‘Loudon’s Gardener’s Mag.,’ vol. iv. 1828, p. 112. [10] Mr. Rivers in ‘Gardener’s Chron.,’ 1866, p. 732 This view that the sleep of leaves saves them from being chilled at night by radiation, would no doubt have occurred to Linnæus, had the principle of radiation been then discovered; for he suggests in many parts of his ‘Somnus Plantarum’ that the position of the leaves at night protects the young stems and buds, and often the young inflorescence, against cold winds. We are far from doubting that an additional advantage may be thus gained; and we have observed with several plants, for instance, Desmodium gyrans, that whilst the blade of the leaf sinks vertically down at night, the petiole rises, so that the blade has to move through a greater angle in order to assume its vertical position than would otherwise have been necessary; but with the result that all the leaves on the same plant are crowded together as if for mutual protection.