CAUSE OF MOTION IN PLANTS. ]]H 



contracts and dilates: but the plant seems much move to 

 depend on the spiral wire. It is impossible not to be struck 

 with astonishment and admiration at the beauty and deli- 

 cacy of the contrivance, which is far more artificial than the 

 works of nature generally are ; and 1 know not a plant, that 

 has taken me so much time, and given me so much trouble, 

 to deveiope the different joints, pulleys, knots, and bolts. I 

 have long perceived, that a plant is sensitive in proportion 

 to the tight manner in which it is twisted, and the fhort dis- 

 tance between the knots : now there is scarcely in this 

 plant T V of an inch between the knots; and the spiral is 

 twisted as tight as possible. I could not persuade myself 

 the sketch was exact, till I had from different specimens 

 drawn it twelve or fourteen times ; but I have exposed the 

 greatest part to. the view of so many friends, that I think I 

 may truly answer for its being exactly sketched after nature. 



At D. fig. 1, PI. IV, are the springs that govern each leaf, Mechanism of 

 d d is the stalk. Each leaf has a base c c, which serves to the leaf, 

 concentrate the spiral wires. These passing over in every 

 direction, being drawn through the narrow part of the stem 

 by the strings bbbb, press the stem together; and, when 

 touched, lay the leaves one on the other the whole way 

 down the leaf stalk. But before the ftimulus is applied; 

 the stem is flattened in a contrary direction. The ball of the 

 leaf is hollow, and filled with oil. The parts e e and p p, 

 PI. Ill, fig. 8, are made of that leathery substance, which 

 forms the cuticle, and is contracted by the light in the solar 

 microscrope, just as the bag of the nettle is acted upon, or 

 the twisting part of the grass. Tlie parts ee contain the 

 oil, which serves to lubricate the knots (I suppose) and en- 

 able them to slip over each other ; beside probably acting 

 some important part in the formation of the various gasses 

 and juices in the composition of the plant. When touched 

 the whole string relaxes at o o, arid lets the branch fall. 

 This it would also do at m, if it was not supported by the 

 wood vessels turning into the leaf. Fi,g. c 2, PI. IV, is the 

 part e e p p, uncut, and in its natural state. The sort of 

 bolts are retained in their places by the wood vessels which 

 cross them in every direction ; as in training plants they 

 do, to defend the bud from accident. I should have placed 



them 



