CAUSE OF MOTION IN PLANTS. 115 



plants wind in their regular order. Nor can the flower 

 opening at a different time of the day, or turning in a diffe- 

 rent manner, militate against the argument; as the constant 

 effect of strong light and dry weather is to contract the 

 wire; that of darkness and moisture, to dilute it; and it de- Spiral wire re- 

 pends wholly on which ivay the spiral wire is placed, whe- opening of tk* 

 ther its dilating shall open or shut the flowers : as in mecha- flower. 

 nics, the same spring may be made to turn to the right or 

 to the left, to open or shut a box. Most of the flowers I 

 have observed, that close at noon, are extremely limber in 

 the corolla, which is formed only of a double cuticle, with- 

 out pabulum, and soon overcome by heat ; and when this is 

 the case, relaxation directly takes place. Such is the con- 

 volvulus nil, the hesperantha cinamomea, the tiger plant, 

 the evening primrose, &c. The great Author of nature 

 shows in all his plans a simplicity, that must hourly strike 

 the dissecter of plants, and prove how much more ability is 

 necessary to produce such simple mechanism, than to invent 

 our more cumbrous machines. 



Mirbel, one of the latest and best of the French botani- 

 cal writers, though his work is one of the first compendiums 

 of the science, has greatly mistaken the subject, merely 

 from not having sufficiently magnified his specimens. He 

 says, " if the spiral wires were common to most plants 

 (which he does not believe) they could not in any way pro- 

 mote the motion of planes, because they are confined in a 

 case which cannot stretch." I shall give an exact drawing Case of the 

 of the case, which will I think plainly prove it was made for s P iral wire 

 no other purpose : but to see this it is necessary to place it in 

 the solar microscope, and Mirbel did not use one. I con- 

 trived to measure its increase by taking it out of a leaf stalk, 

 and placing it between a double pair of pincers, which 

 were laid in a groove, moving them by means of a thread 

 over a very little wheel. They were drawn with a delicacy 

 no hand could imitate, and it stretched without breaking 

 (by moistening it) from 1 inch and a quarter, to 2 inches 

 wanting 2 tenths, but it was after being apparently much 

 contracted by light in the microscope. As to the spiral wire made t® 

 it is apparent, that it may be drawn to any length. A larger stretch * 

 magnifier would also have convinced Mirbel, that the case 

 12 is 



