1876.] 



on the Leaf of Dionsea muscipula. 



433 



giving, as means, for the midrib 0-27, for the bridge 0'58. In another 

 leaf similar comparisons were made between the excnrsiou at the outer 

 surface of the left lobe opposite the hairs and the bridge, with these 

 results : — 



On the outside 0-26, 0-24, 042, 0-18. 



On the bridge 0*87, 0-65, 0'85, 0-83. 



In these instances the distance traversed by the wave of negative varia- 

 tion was not even so great as in the cases in which its progress was 

 investigated from one side of the leaf to the other ; so that it might, at 

 first sight, be inferred from the much greater prolongation of the delay 

 that the rate of transmission was slower towards the root of the leaf than 

 across it. It is possible that it is so, but it cannot be inferred from the 

 measurements ; for in the case of the observations relating to the bridge 

 two excursions are compared of very different intensity ; and when this 

 is the case the weaker one appears to be behind the other, and is, in fact, 

 seen last even when the two culminate simultaneously. 



The time at which the mercurial column reaches its furthest point 

 (acme of excursion), and the time at which it returns to its original posi- 

 tion, have been severally determined in a considerable number of instances 

 in normal leaves. The results are embodied in the following Table. 

 All of them relate to observations in which the fixed contact was at the 

 external surface of the leaf, viz. in four cases on the outer surface of 

 a lobe, in four cases on the midrib. In all the cases the excitation was 

 mechanical, and the hairs touched were in the immediate neighbourhood 

 of the contact. 



Table IV. 

 Time, in seconds, after excitation of 





No. 



of leaf. 



Beginning 

 of 



excursion. 



Maximum 

 of 



excursion. 



End of 

 excursion. 



Number 

 of obser- 

 vations. 



Outer [ 

 surface of-( 

 lobe. 1 



I 

 ( 



]\Iiclrib. { 

 1 



I 



a 

 h 

 c 



Do. cTiflf. 1 

 contact. / 



a 



cl 



e 



f 



0-17 

 0-12 



0:20 : 



0-22 



0-27 

 019 

 0-17 

 0-23 



Not observed. 

 1-06 



0- 99 



1- 44 



Not observed. 

 Do. 

 1-34 

 1-46 



216 

 2-01 



1- 81 



2- 69 



1-51 

 1-59 

 Not observed. 

 2 '22 



7 



4 

 8 



7 



7 



4 

 3 

 3 





Means 



0-19 



1-26 



1-99 





From this Table the general conclusion may be drawn that in normal 

 leaves, in which the excursion begins to be appreciable by the electro- 

 meter at the external surface, at about a sixth of a second after mechanical 

 excitation, the excursion attains its maximum in one second, and that its 



