358 PHYTOLOGT. 



of the leaf has an equal motion through its whole length, and it appears 

 to be nearly equal on all sides ; for in its various motions the lobed 

 part is bent towards that side where the plant bends ; it performs a kind 

 of conoid motion. 



To see if the actions of plants were affected by a continuation of 

 stimulus similar to those of animals, I made the following experiments. 



As I took for granted that the analogy could go no further than as it 

 related to the actions produced by external stimuli, my experiments 

 were only made on such plants as exhibited actions of this kind. 



As those parts of plants which are capable of the second and third 

 kinds of motion are generally small, as leaves, tendrils, flowers, &C 1 

 it is difficult to discover the mechanism upon which the motions depend : 

 the sensitive plant is probably the best of this kind that we are as yet 

 acquainted with. As the motion of the petioles is confined principally 

 to one part, and that differing from the others in external appearance, 

 which difference is its increased thickness and uniformity of surface, 

 upon cutting the footstalk longitudinally, as also the stem on which 

 it stands through its whole length, the following appearances may be 

 observed 2 : — 



For the purpose of making my experiments I took three sensitive 

 plants, having several others for any comparative experiments which 

 might be thought necessary. I first pitched upon one leaf in each plant 

 which was capable of the greatest motion of collapsing and erection ; 

 and behind each of these leaves a board was placed, on which was 

 marked the greatest extent of the two motions, so that the leaf was like 

 the index or radius of an arc. 



To have the greatest part of the day before me, I began my experi- 

 ments at eight in the morning, while the leaves were in full expansion, 

 and I continued them till four in the afternoon, as longer than this 

 would not have been just, for they begin to collapse of themselves 

 between five and six o'clock. 



1 [The stamens of certain plants offer striking examples : those of Saxifraga 

 approach in regular succession the pistil, and as soon as each has shed its pollen 

 over it, it retires and gives place to another. The stamens of the barberry show 

 more active movements. In the tiger-lily the pistil pends first to one stamen and 

 then to another.] 



2 [A blank in the manuscript here occurs, which leaves us ignorant as to the result 

 of Hunter's examination of the structure of the irritable intumescence at the base 

 of the leaf-stalks and stalklets of the Mimosa. With his usual sagacity, however, 

 he rightly refers the motive power to this part, and it has since been the subject of 

 much diligent and minute investigation.] 



