102 



MOVEMENTS OF CURVATURE 



most Leguminosae and Oxalidaceae, as well as by the leaves of Marsilea, 

 Porliera, Portulaca, and Phyllanthus Niruri. It can be seen from Fig. 28 

 that Desmodium gyrans allows the leaf laminas to droop so that the stalks 

 rise up when night falls, and hence assumes quite a different appearance. 

 The three leaflets of Oxalis acetosella x droop downwards around and against 

 the petiole, whereas the leaflets of Trifolium fold together upwards, and then 

 the upper end of the petiole curves laterally or downwards. In the case of 

 the pinnate leaves of Amorpha and Robinia the leaflets droop downwards 

 at night and press their under-surfaces together (Fig. 29) whereas those of 

 Acacia lophantha and Mimosa pudica fold upwards in pairs with the dorsal 

 surfaces together 2 . Since at the same time the main petiole of Mimosa 



pudica sinks, the position 

 assumed resembles closely 

 that produced by a me- 

 chanical excitation (Fig. 

 19, p. 61). If the plant is 

 highly turgid the pulvinus 

 may when mechanically 

 excited during the early 

 hours of the tropical night 

 show an additional curva- 

 ture and may bend the 

 leaf backwards across the 

 stem and. support it for 

 a short time upside down 

 against the action of gravity . 

 This excessive movement 

 is not always shown, and 

 later on the normal droop- 

 ing position is again as- 

 sumed 3 . It is only in cer- 

 tain cases that, in addition to its photonastic excitability, the leaf-pulvini 



FIG. 29. Leaf of Amorfihafruticosa. A in day position, B in 

 night position. 



1 The leaflets assume the same position as after mechanical excitation. Cf. Fig. 20, p. 62. 



8 A summary of the plants showing sleep-movements is given by Hansgirg, Physiolog. u. 

 Phycophytolog. Unters., 1893; Neue Unters. iiber den Gamo- u. Karpotropismus, sowie iiber Reiz- 

 u. Schlafbewegungen, 1896 (Sitzungsb. d. bohmisch. Ges. d. Wiss.) ; Beihefte z. botan. Centralbl., 

 1902, Bd. xii, pp. 267, 272. Cf. also Pfeffer, Periodische Bewegungen d. Blattorgane, 1875, p. 159, 

 and'the literature there quoted. Numerous facts and figures are given by Darwin, The Power of 

 Movement in Plants, 1880 ; Kerner, Natural History of Plants, 1895, p. 534. For additional facts 

 see Popow, Bot. Jahresb., 1880, p. 278 (Gleditschia) ; Bruckner, Bot Centralbl., 1882, Bd. XII, 

 p. 171 ; Vochting, Bot. Ztg., 1888, p. 519 (Malvaceae) ; F. W. Oliver, Bot. Centralbl., 1891, Bd. 

 XLV, p. 52 (Abrus) ; Paoletti, Nuov. giornal. hot. ital., 1892, T. xxiv, p. 65 (Porlierd} ; Mobius, 

 Bot. Centralbl., 1894, Bd. xv, p. 8 ; Jost, Bot. Ztg., 1897, p. 17 ; Jahrb. f. wiss. Bot., 1898, Bd. xxxi, 

 p. 345 ; Ewart,^Annals of Botany, 1897, Vol. XI, p. 439 ; Stahl, Bot. Ztg., 1897, p. 85 ; Linsbauer, 

 Ber. d. bot. Ges., 1903, p. 27. 



3 Ewart, 1. c., p. 453. 



