LECT. XI.] CAULINAR AND FOLIAR APPENDAGES. 677 



taneous movement, either asserts too much, or has 

 no meaning: for if, by spontaneous motion, we 

 do not imply a power of volition in the moving 

 agent, a power I am certainly not prepared to ad- 

 mit as an attribute of plants, we must use some 

 other term to express our meaning. 



The deficiency of correct observations on the 

 habits of the plant is, probably, the chief reason 

 why no satisfactory theory of this phenomenon 

 has yet been advanced. Thus, if it had been 

 observed, that the lid opened every morning and 

 closed every night, its elevation might be reason- 

 ably ascribed to the stimulus of light, acting on 

 its irritability, and exciting such an increased 

 action of the vessels as would produce that af- 

 flux of fluid which has been supposed to oc- 

 casion its erect position; and its depression, to 

 the withdrawing of this exciting cause: for, as 

 the lid is really a leaf, and its hinge an arti- 

 culation closely resembling that which connects, 

 with the common petiole, the leaflets of those 

 pinnated leaves which fold together their leaflets 

 at night, we might regard its movements as the 

 result of the same cause which produces the 

 diurnal motions of these leaflets. But we have no 

 evidence that this daily change of position of the 

 lid occurs: we are informed that it opens when 

 the weather is showery and damp as well as at 

 night ; and I am disposed to think that the heavy 



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