SPONTANEOUS MOVEMENTS IN PLANTS. 345 



governed by it. The so-called sleep of (lie common Sensitive Plant, 

 lor instance, begins just before sunset, but its waking frequently pre- 

 cedes the dawn of day ; showing that it is not the mere amount of 

 the light which governs the position, in the manner of a mechanical 

 power.* 



673. Sensible Movements from Irritation. All the changes of posi- 

 tion already described — like those of the hands of a clock or of 

 the shadow on a dial — are too slow for the motion to be directly 

 seen. But a greater exaltation apparently of this common faculty 

 is observed in the leaflets of various Leguminous plants, especially 

 of the Mimosa tribe, which, when roughly touched, assume their 

 peculiar nocturnal position, or one like it, by a visible and sometimes 

 a rapid movement. The Sensitive Plant of the gardens (Mimosa 

 pudica) is a familiar instance of the kind, suddenly changing the 

 position of its leaflets on being touched or jarred, and applying 

 them one over the other close upon the secondary petiole ; if more 

 strongly irritated, the secondary petioles alfo bend forward and 

 approach each other, and the general petiole itself sinks by a bend- 

 ing at the articulation with the stem. Similar although less vivid 

 irritability is shown by the Mimosa strigilloia and the Schrankia of 

 the Southern States, where the leaflets promptly fold up when 

 brushed with the hand. The most remarkable instance of the kind, 

 however, is presented by another native plant of the United States, 

 the Dionsea muscipula, or Venus's Fly-trap (Fig. 297, 298) ; in which 

 the touch even of an insect, alighting upon the upper surface of the 

 outspread lamina, causes its sides to close suddenly, the strong 

 bristles of the marginal fringe crossing each other like the teeth of 

 a steel-trap, and the two surfaces pressing together with considerable 

 force, so as to retain, if not to destroy, the intruder, whose struggles 

 only increase the pressure which this animated trap exerts. This 

 most extraordinary plant abounds in the damp, sandy savannas in 

 the neighborhood of Cape Fear River, from Wilmington to Fayette- 



* The odors of flowers, also, arc sometimes given off continually, as in the 

 Orange and the Violet, or flowers may nearly lose their fragrance during the heat 

 of mid-day, as in most cases ; while others, such as Pelargonium triste, Hesperis 

 tristis, and most dingy flowers, which are almost scentless during the day, ex- 

 hale a powerful fragrance at night. The night-flowering Ccreus grandiflorus 

 emits its powerful fragrance at intervals ; sudden emanations of odor being 

 given ofF about every quarter of an hour, during the brief period of the expan- 

 sion of the flower. 



