MOVEMENTS OF PLANTS. 



653 



turgescence are not clearly determined. The spontaneous and induced 

 motions, according to Bert, are differently affected by the same conditions. 

 Bert and Millardet also show that the spontaneous movement in the 

 Mimosa is not confined to depression, followed after a period "by elevation, 

 as in most cases of plants whose leaves sleep ; but the movements in 

 question are more or less continuous, the one alternating with the other. 

 "Unlike most plants, the Sensitive Plant raises its leaves at night, and 

 lowers them by day. 



Nature of the Movements. The most common kind of movement is 

 that in which leaves or floral envelopes return to the position which 

 they originally occupied, or close up into the same folds which they 

 exhibited in the buds. 



Compound leaves, like those of Leguminosse for instance, display a 

 simple or compound movement j in the Bean (Faba vulgaris) the leaves 

 fold upwards, in Lupinus downwards, in Tamarindus to the side. In 

 Amorpha fruticosa and Gleditschia triacanthos the rachis or common 

 petiole of the compound leaves rises or sinks, while the leaflets turn 

 downwards or to the side. In Mimosa pudica the leaflets fold together, 

 the partial petioles approach each other, and the rachis or main petiole 

 sinks down. In a species of Oxalis the pinnate leaves are folded toge- 

 ther in an upward direction, a footfall sufficing to cause the plant to close 

 its leaves (figs. 615, 616). 



Fig. 615. 



Fig. 616. 



Fig. 617. 



X.4* 



Fig. 615. Plant of Oxalis. 



Fig. 616. The same species, with the leaves erect and closed, as a consequence of irritation, or 



in "sleep." 

 Fig. 617. Leaflet, magnified. 



When such movements of leaves or foliaceous organs occur at parti- 

 cular hours, and the structures remain in the new position until the 

 recurrence of a particular period, the closing up is called the sleep of plants, 

 which is observed both in green leaves and in the petals of flowers. 



