■86 PERIODIC MOVEMENTS AND THOSE DUE TO IRRITATION. 



the movements of the compound leaves of Leguminosae, of many species of Oxalis, and of 

 Marsilea. In the Leguminoss the common petiole is often attached to the stem by a 

 larger contractile organ or 'puHnnus'\ and in all the cases just named the petiolule of each 

 leaflet possesses a similar organ. If, as in the bipinnate leaves of ISIimosa, there are 

 secondary common petioles, these are also attached to the primary petiole by contractile 

 organs. These organs always consist of an axial fibro-vascular bundle surrounded by a 

 thick layer of turgid parenchyma. The other parts of the leaves, the petioles as well 

 as the lamina, are not spontaneously contractile, but the alterations in their length are 

 caused by the curvatures of the organs at their base. The movement is either a curving 

 upwards and downward s as in Phaseolus, TrifoHum, Oxalis, and the common petioles 

 of Mimosa, or is directed from behind and below in a forward and upward direction, 

 as in the leaflets of Mimosa. 



(2) The phenomena known as Waking and Sleeping are exhibited with peculiar dis- 

 tinctness in the leaves of Leguminosae and Oxalidea^ and of Marsilea, and are caused by 

 the organs which also produce the spontaneous periodic movements'. They occur also 

 in the leaves of many other plants as Scitamineae, where the lamina is attached to the 

 petiole by a similar cylindrical contractile organ, as well as in many leaves (especially 

 also in green cotyledons) the petiole and lamina of which do not possess a sharply 

 differentiated prominent contractile organ ; in these cases the movements of sleeping and 

 waking are occasioned by the basal and apical portions of the petiole. It is not known 

 whether these leaves are also endowed with automatic periodic motion. In all these 

 green leaves the movement is caused principally by the alternation in the intensity 

 of the light, and especially by that of the strongly refrangible rays^ ; every increase of 

 intensity causing a movement in the direction of the diurnal position, every decrease one 

 in the direction of the nocturnal position. 



In the diurnal position of these organs the leaves generally have their surfaces com- 

 pletely unfolded and expanded flat ; in the nocturnal position they are on the contrary 

 folded up in different ways, being turned upwards, downwards, or sideways. The leaflets 

 of Lotus, Trifolium, Vicia, and Lathyrus are, for example, folded upwards at night, those 

 of Lupinus, Robinia, Glycyrrhiza, Glycine, Phaseolus, and Oxalis downwards ; the com- 

 mon petiole of Mimosa turns downwards at night, that of Phaseolus becomes erect ; the 

 leaflets of Mimosa and Tatnarindus indica^ turn laterally forwards and upwards in the 

 dark, those of lephrosia carabica backwards. When the petiole and other parts of the 

 same leaf are contractile, the curvatures of the various motile parts may differ ; thus, for 

 example, the petiole of Phaseolus turns upwards in the evening, while the leaflets turn 

 downwards ; the petiole of Mimosa on the other hand turns downwards while the leaf- 

 lets turn forwards and upwards, till they partially cover one another in an imbricate 

 manner. As the periodic movement of leaves, and that of sleeping and waking must be 

 distinguished from revolution caused by growth, which makes them unfold, so in flowers a 

 distinction must be drawn— which is not always done ^—between mere unfolding and the 

 periodic movements of sleeping and waking. Petals which, after opening and remain- 

 ing open for some time, simply fall oft" or wither (like those of IVlirabilis, Cereiis grayidi- 

 Jlorus, Helianthemum imlgare, &c.) are not included in this category. There are others 

 however^ which last for some days and alternately open and close, usually in the evening 

 and morning or on a change of weather, as e. g. those of Tulipa, Crocus, the potato, 

 Oxalis, Mesembryanthemum, Ipomsea, Convolvulus, Hemerocallis, Portulaca, &c. The 



^ [See Somnus Plantarum, P. Bremer, Linn. Amcen, Acad. iv. p. 333. — Ed.] 

 2 See Sachs, Bot. Zeit., 1857, p. 813. 



^ See Meyen, Neues System der Pflanzen-Physiologie, vol. III, p. 476. 

 * Compare Dutrochet, Memoires pour servir, 1837, vol. I, p. 469 et seq. 



' [See Linnceus, Philoiophia Botanica, ed. 1780, pp. 272-275; K. Fritzsch, On die Periodical 

 Opening and Closing of Flowers, Journ. Hort. Soc. Lond. vol. A'JII, 1853. — Ed.] 



