CAUSE OF MOTION IN PLANTS. \\J 



ceive me, before I deceive others. 1 have now to present 

 three of the most sensitive plants I am acquainted with, in 

 order to show the full strength of the spiral wire, and of 

 that sort of leathery substance of which it is composed. 

 The first is the Indian grass that conducts the hygrometer 

 made by Captain Kater; the second is the thorn of the net- 

 tle, which is certainly made of the same leatherlike sub- 

 stance ; and the third is the mimosa sensitiva, the bag of 

 which plant is also of the same nature, though infinitely 

 thinner. They are all governed by this substance turned 

 into a spiral wire, and the same substance in another form. 

 When thicker it is certainly infinitely stronger, as it proves 

 bj r the awn of the grass, which is so powerful, though much 

 of it has lost its spiral wire. There is a water plant that 

 sends up its flower by the same substance, and which J have 

 not been able to procure; but I shall be satisfied with 

 showing the dissection of these plants, perfectly convinced 

 they will be thought sufficient to prove, that this stibstance 

 is the cause of motion in plants. 



The first is an Indian grass, but the only part sensitive is Formation of 



the awn, which is formed of this leatherlike substance, in- J^eawnofthe 



• i • - Indian grass. 



finitely thicker and stronger than the usual spiral wire, and 



its untwisting would be certainly .capable of regulating a 

 much more powerful instrument. The awn is formed of 

 two apparently flat pieces, with a cylindric hollow running 

 through the middle, which is filled with a thick spiral wire, 

 but which I have found in oply two pieces : the rest (I sup- 

 pose from long keeping) must hav.e decayed. Each side is 

 bristled as the awns of grass generally are, but J never could 

 perceive, that these bristles added any sensitive power to 

 the awn, though from their resembling those in the .sensitive 

 plant I expected to find that they did. I therefore deprived 

 both plants of this ornament; but I could not perceive any 

 difference in their sensibility, and in neither specimen are 

 tl\ey twisted. It is quite wonderful to see the strength with 

 which this wire twists and untwists. It is only the very 

 finest part, that can be placed in the solar microscope, 

 without breaking the glasses between which it is laid, though 

 not three tenths of an inch in length. What is extraordi- 

 nary is, that so made, it will continue to untwist into two The unta's* 



different 



