525 The Sensitive Plant. [November, 



[acacia mimosa.] 



In its native country, Brazil, this singular plant grows to tlie higlit 

 of seven or eight feet, and is armed with short recurved thorns; the 

 leaves grow upon long foot-stalks, which are prickly, each sustaining 

 two pairs of wings— from the place where these are inserted come 

 out small branches, having three or four globular heads of pale pur- 

 plish flowers, coming out from the side on short peduncles. Natu- 

 ralists, says Dr. Darwin, have not explained the immediate causes of 

 the collapsing of the sensitive plant ; the leaves meet and close in the 

 night, during the sleep of the plant, or when exposed to too much 

 heat in the day time, in the same manner as when they are afi"ected 

 by external violence, folding their upper surfaces together, and in 

 part over each other, like scales or tiles, so as to expose as little of 

 the upper surface as may be to the air ; (many of the acacia do this 

 wdiich are not otherwise sensitive ;) but do not, indeed, collapse quite 

 so far, for when touched in the night, during their sleep, they fall 

 still farther, especially when touched on the footstalks, between the 

 stem and the leaflets, which seem to be their most sensitive or irrita- 

 ble part. Now as their situation, after being exposed to external 

 violence, resembles their sleep, but with a greater degree of collapse, 

 may it not be owing to a numbness or paralysis consequent on too 

 violent irritation, like the faintings of animals from pain or fatigue ? 

 A sensitive plant being kept in a dark room till some hours after 

 day-break, its leaves and leaf-stalks were collapsed as in its most pro- 

 found sleep, and on exposing it to the light, above twenty minutes 

 had passed before the plant was thoroughly awake and had expanded 

 itself During the night the upper surface of the leaves are oppress- 

 ed : this would seem to show that the office of this surface of the 

 leaf was to expose the fluids of the plant to the light as well as to the 

 air. If kept in the dark it fails to expand during the entire day.— 

 Although easily grown by any one, simply requiring to be treated 

 as a tender animal, there is no plant we grow requiring so little trou- 

 ble, that excites such a lively interest, and been seen by so few peo- 

 ple, as this sensitive plant. Dr. Darwin thus characterizes this plant 



in verse : 



" Weak with nice sense, tlie chaste Mimosa stands. 

 From each rude touch withdraws her timid hands ; 



