IIS CAUSE OF MOTION IN PLANTS. 



ingtheawnof different threads, and T donbt not at last separate into as 

 fine a wire as runs in the mimosa. The hydrometer made 

 of it is the best that was ever invented, and indeed it is dif- 

 ficult to conceive one more sensible, since at nearly an inch 

 distance the moisture of a ringer will cause it to make one 

 or two revolutions of 100 parts each. The figure of the in- 

 strument was given in your Journal for last July. 

 Formation of The next plant is the nettle, irritable only at the aivn or 

 the nettle. sting of the plant. It is a long pipe with a bag at the end, 

 divided into two parts; the smaller, in which is enclosed 

 the bag of the poison ; and the larger, which is below it. 

 The whole bag appears to be formed of the same leather- 

 like substance as the awn of the grass, and to be, in pro- 

 portion to its size, equally affected by light and moisture. 

 The moment the upper part of the pipe is touched, the 

 under part of the bag whirls up, breaks the poison bladder, 

 and throws its contents violently up the pipe, burning the 

 person who touches it. This is instantaneous ; and so sus- 

 Sffectof light ceptible is it, that the light thrown on it in the solar micro- 

 theMcule"" ° sc0 P e nas exactly the same effect as the touch. The liquor 

 is protruded with a force quite wonderful up the pipe, till 

 it issues at the minute aperture of the point; but before it 

 does so, the pipe is bent down with a jerk by the spiral 

 wire, exactly as the leaf stalk of the mimosa sensitiva bends 

 to the touch. They are managed exactly by the same force, 

 and governed by the same powers, light and moisture. This 

 description of the nettle will account for its not stinging 

 when pressed hard ; the pipes being then broke, and the li- 

 quor of the nettle, mixing with the poison, dilutes it so 

 completely, that it has no longer any effect. It will be seen, 

 that the spiral wire is carried round the bag, and that it is 

 Lays down its drawn together by the contraction of the wire: and to corn- 

 stings at night. pj e ^ e ^| je likeness of the three plants! must mention, that 

 the nettle lays clown its large stings every evening just as 

 the sensitive plant does its branches, and that the awn of 

 the grass slso untwists towards evening. 

 Sensitive plant. I shall now turn to the mimosa sen ,tiva, which has less of 

 real strength, but more mechanism than the other two. Its 

 motions proceed from the saint: cause, which is not only 

 the spiral wire, but a bag of the same leathery kind, that 



contracts 



