ON THE STEM OF TREES. 343 



hardened coin ? But the mind that is accustomed to see them 



in their first delicate forms produce great effects, will not 



doubt what the Almighty power may fit them for. 



In detailing the arguments that tend to prove, that the Argument from 

 » » t Rater's hygro- 



spiral wire is the cause of motion in plants, 1 must suggest me ter, that the 



one, which will at least clear it from all improbability. To s P ir » l wire y th * 

 ' 7 , , , ,. , motive organ. 



those to whom the energy, strength, delicacy, and suscep- 

 tibility of Captain Kater's hygrometer is known, it will 

 offer a certain proof of the possibility of such an existing 

 power; since that little instrument is acted upon by the 

 power moisture has of untwisting the awn of a grass brought 

 from India. Now if the most trifling change of moisture 

 can untwist one sort of vegetable fibre, and by this means 

 manage an instrument, why should not a quantity of simi- 

 larly formed fibres or spiral wires produce the same effect 

 on leaves and flowers? Captain Kater's hygrometer moves 

 very sensibly if a finger is placed within half an inch of the 

 fibre: now the most sensiti?e plant we have will not move 

 but with the touch: though I doubt not in its natural soil 

 and climate it is more sensible : but in the sensitive plants 

 there is a peculiarity in the joint, which helps to produce 

 that regularity of movement which is the most curious cir- 

 cumstance in its formation ; this I hope to explain in my 

 next. My only doubt is, I confess, whether the power 

 that governs the spiral wire is light, heat, or moisture? I 

 am rather inclined to think it is moisture ; though of course 

 light and heat must have very great influence, as no change 

 of either can happen, without its increasing or diminishing 

 the moisture of the atmosphere. 



I fear I have tired the reader ; but I have not produced Flowers, 

 half the proofs I might bring forward to show, u that if 

 the spiral vessels are the origin of motion in both leaves and 

 flowers," flowers may be made to change their position with 

 every variation of light and heat, even more than leaves; 

 and in the acacia I have made the leaves and flowers droop 

 in the middle of the day, by holding a wet napkin sus- 

 pended over them after I had completely shaded them; and 

 by carrying flowers into an ice house.* they will distinctly 

 prove what part is affected. 



The 



