318 



DIONJiA MUSCirULA. 



CHAP. XIII. 



dots now stood about 



1000 



of an inch ('127 mm.) 



nearer together than before. If we suppose the whole 

 upper surface of the lobe, which was Vo'Vo of an inch 

 in breadth, to have contracted in the same proportion, 

 the total contraction will have amounted to about 

 T I g or -JIT f an i ncn ('635 mm.) ; but whether this 

 is sufficient to account for the slight inward curvature 

 of the whole lobe, I am unable to say. 



Finally, with respect to the movement of the leaves, 

 the wonderful discovery made by Dr. Burdon Sander- 

 son* is now universally known ; namely that there 

 exists a normal electrical current in the blade and 

 footstalk ; and that when the leaves are irritated, the 

 current is disturbed in the same manner as takes place 

 during the contraction of the muscle of an animal. 



The Re-expansion of the Leaves. This is effected at an 

 insensibly slow rate, whether or not any object is 

 enclosed.! One lobe can re-expand by itself, as oc- 

 curred with the torpid leaf of which one lobe alone had 

 closed. We have also seen in the experiments with 

 cheese and albumen that the two ends of the same lobe 

 can re-expand to a certain extent independently of 

 each other. But in all ordinary cases both lobes open 

 at the same time. The re-expansion is not determined 

 by the sensitive filaments ; all three filaments on one 

 lobe were ut off close to their bases ; and the three 



* * Proc. Royal Soc.' vol. xxi. 

 p. 495 ; arid lecture at the Royal 

 Institution, June 5, 1874, given in 

 'Nature,' 1874, pp. 105 and 127. 



t Nuttall, in his ' Gen. Ame- 

 rican Plants,' p. '217 (note), says 

 that, whilst collecting- this plant 

 in its native home, " I had occa- 

 sion to observe that a detached 

 leaf would make repeated efforts 

 towards disclosing itself to the 



influence of the sun ; these at- 

 tempts consisted in an undula- 

 tory motion of the marginal cilias, 

 accompanied by a partial open- 

 ing and succeeding collapse of 

 the lamina, which at length ter- 

 minated in a complete expansion 

 and in the destruction of sensi* 

 bility." I am indebted to Prof. 

 Oliver for this reference ; but I da 

 riot understand what took 



