ON I HE &TBM OP TREE*. 



341 



their former position ; reverse it, and it will now want dou- 

 ble the time to bring them right; change the order a third 

 time, and though the plant will not in any manner have 

 suiFered, yet the leaves will be long regaining their pristine 

 force. Few can move after the third or fourth regression ; 

 and why? because the spiral, like elastic vessels, were so. 

 relaxed by the operation, as to have lost all power of coil- 

 ing into their usual form. 



3d. I have observed that those leaves, that have the most Most motion ia 

 motion, have also the most of these spiral vessels, and have^J tested. 

 them most twisted. This is particularly seen in the populus 

 iremula; the leaf stalk, though small, is full of them, and 

 so hard twisted, that I have known the stalk to measure a 

 quarter of an inch difference in length between the middle 

 of the day and a cold evening. This could arise only from 

 the untwisting of the spiral wire; and few plants have more 

 motion, indeed it has far more than can fairly be attributed 

 to its long leaf stalk. 



4th. I took a vine leaf, and without separating it from Leaves neither 

 its parent plant, I merely divided the spiral vessels, without *" r " nor .™? vc 

 touching the nourishing ones; it never from that moment wires be cut. 

 either turned, or contracted; and when placed with its back 

 to the light, it remained in this position, though it was long 

 before it decayed. Both electricity and galvanism draw up 

 these leaves, as if they were leather: but it is the spiral 

 fibres, not the cuticles ; for after I took from a leaf all the 

 6piral wire, the leaf did not contract at all. Bonnet was Bonnet's coo- 

 convinced, that all the motion of plants might be given bjr tri:vance * 

 the means of -threads, but microscopes were not so perfect 

 then as to give him the delight of knowing, that he had, 

 guessed the operations of nature. He made an artificial 

 leaf and flower, that would move by the contrivance of 

 threads that passed through all the larger vessels, and by 

 this means they effected every movement common to either. 

 But his were plain threads, not a spiral wire, the elastic 

 power of which is well known to every person : nor had 

 he an idea, that such vessels existed, but thought it was the 

 contraction and elongation of tha upper and under cuticle 

 of the leaf; but this is certainly not the case, «as I have , 

 proved abose, that it ha* ?io such powers. There arc in- 

 sects 



