256 ItEMAUKS ON THIi SENSITIVE PLANT. 



situated in the last articulation are of sufficient size to be submitted 

 to experiment. If, by a longitudinal section, the lower half of this 

 swelling be removed, the petiole will remain depressed, having lost 

 the power of elevating itself: if the superior half be removed, the 

 petiole will remain constantly elevated, having lost the power of 

 depressing itself. These facts prove that the motions of the petiole 

 depend on the alternate turgescence of the upper and lower half of 

 the enlargement, situated at the point of articulation : and that con- 

 tractibility is not the principle of these motions. 



If one part of the plant be irritated, the others will soon sympa- 

 thise, or bear witness, by the successive falling of their leaves, that 

 they have successively felt the irritation. — Thus, if a leaflet be burnt 

 slightly by a lens, the interior movement which is produced will be 

 propagated successively to the other leaflets of the leaf, and thence to 

 the other leaves on the same stalk. A very clever French, experi- 

 mentalist, Mons. Dutrochet, found, 



1st. That this interior movement is transmitted equally well, either 

 ascending or descending. 



2nd. That it is equally well transmitted, even though a ring of 

 bark has been removed. 



3rd. That it is transmissible, even though the bark and pith be 

 removed so that nothing remain to communicate between the two parts 

 of the skin, except the woody fibres and vessels. 



4th. That it is transmissible, even when the two parts communi- 

 cate merely by a shred of bark. 



5th. That it may be transmitted, even when the communication 

 exists by the pith only. 



6th. But that it is not transmissible, when the communication exists 

 merely by the cortical parenchyma. 



From these very interesting experiments, it results that the interior 

 movement produced by irritation, is propagated by the ligneous fibres 

 and the vessels. 



The propagation is more rapid in the petioles than in the body of 

 the stem ; in the former it moves through a distance of from three to 

 six tenths of an inch in a second ; in the latter, through from eight 

 to twelve hundredths of an inch, during the same portion oP time. 

 External temperature does not appear to exert any influence on the 

 rapidity of the movement, but very sensibly affects its extent. 



Absence from light, during a certain time, completely destroys the 



