many mporlant Truths in Phyiology. 109 



the Spiral wire keeps them, aided by the. wind, produces an eter- 

 nal change in the air around eacli tree. But for this, the oxygen 

 tliey give out would remain (owing to its weight) under the 

 plant: but the muscles agitating its multiplied little fans, mix 

 all the different gases together, and keep them when the wind 

 fails in eternal agitation. All the mechanism of the leaf is ma- 

 naged not only by the same stripes as the petals, but by the 

 mechanical contrivance of the leaf-stalk. It is the gatherer on 

 each end of the peduncle that is the chief source of motion in 

 the leaves. It is but watching this for a few hours, to see all its 

 diiterent motions, and to be convinced it is to the i;piral it owes 

 them, and all its strength also. The stem of the plant possesses 

 not one-tenth part of the motion of the peduncle, nor has it a 

 quarter of its spiral wire, its portion of muscles being exactly 

 equivalent to the action it is obliged to exert. In those leaves 

 that must necessarily turn, follow the motions of the sun, open 

 and close in the morning and evening, there are always more 

 muscles than in the plants that do not open and close. Those 

 plants that do not move their leaves have no spiral wire, such as 

 X\\e firs, lichens, sea iveeds, kc. ; but the coiifervas, that move 

 like a worm and twist hi every direction, are, like the tendrils, 

 composed almost wholly of rtmscles. Take the spirals out of the 

 peduncle; nay, take only a few cf them, and the leaf turns no 

 more : take them out of the tendril, and it becomes perfectly in- 

 ert : — but the spiral you have taken from thence, moves on the 

 glass for hours. 



Can more and stronger proofs be given? Those leaves which 

 have most motions have most spiral wire, and have it most twisted; 

 and if the spiral is taken from the plant, it is perfectly inert, 

 while the part taken from it moves eternally. These proofs, add- 

 ed to the vis insila of the spiral, must, I think, be aJiowed to be 

 as positive evidence as we generally are able to procure of that 

 which is allowed to be true; and therefore sufficient to enable 

 me with confidence to say that the spiral wire is proved to be 

 the muscle of the plant; and that therefore Mr. Knight's idea of 

 the return of the sap must be a mistake, since the vessels he 

 fixed on for the purpose are incapable of carrying any liquid ex- 

 cept a little oil — being the muscles of the plant — and that there- 

 fore there is no circulation of the sap; but that the larger vessels 

 are bark -vessels, which can convey no sap, but are full of bark- 

 juice: — that on a thorough examination of the bark, there are but 

 the inner bark-vessels which run down the tree, all the rest 

 moving round it. I hope, therefore, I shall be thought to have 

 proved the three propositions I undertook to show. 



In my next I shall show the three following, with the same 

 degree of truth. I should apologize for the slylc; but it is dif- 

 ficult 



