1876.] on the Leaf of Dionsea muscipula. 431 



Table I LI. 



No. of 

 Leaf. 



Date. 



Mean 

 tempera- 

 ture of 

 day. 



Mean delay 

 in seconds. 



Number of 

 observations. 





Aug. 21 



64-7 F. 



0-24 



5 



i 





64-7 



0-26 



13 



i 



Oct. I'i 



57-7 



0-23 



3 



k 



„ 19 



56-4 



0-23 



3 



I 



„ 21 



46-4 



0-48 



6 



m 



„ 22 





0-33 



2 



Combining the numbers contained in the two Tables, we have 0*295 as 

 the mean delay at midrib, 0-231 as the mean delay at the outer surface 

 of the lobe when the seat of excitation is close to the contact at which 

 its effect is observed, and lastly 0*403 as the delay when the electrical 

 disturbance has to make its way through the midrib from the opposite 

 side of the leaf ; so that 0-17, or one sixth of a second, is the time 

 required for the transmission of the effects from one side to the other. 

 All the observations on which these numbers are founded were made by 

 mechanical stimulation. In a few experiments we substituted stimula- 

 tion by single induction-shocks, modifying our apparatus by introducing 

 the electro-magnetic chronograph into the primary circuit, so that the 

 moment of its closure was recorded on the cylinder. The results we 

 obtained were remarkably uniform, and confirmed those already recorded. 

 Thus in four observations in which the needle-points were inserted into 

 the outer surface of one lobe close to the movable contact, the intervals 

 were respectively 0*25, 0*25, 0*28, 0*25. When they were inserted into 

 the opposite lobe of the same leaf they were 0*42, 0*49, 0*52, 0-48, 0*56, 

 0-45, 0-54, 0-52, 0-50, 0-46, 0-55. The mean gives 0-18 as the time 

 which the variation takes in order to cross from one side to the other. 

 If we assume the distance thus traversed by what we may call the wave 

 of negative variation to be 8 millims., more or less, we have the rate of 

 propagation about 4*4 centims. per second, that is 600 times as slow as 

 in nerve. This estimate is, no doubt, too low ; for some of the observa- 

 tions were made in cool weather, and we now know that the process is 

 much affected by temperature. If we take as our basis, observations 

 made under the most favourable circumstances in this respect, we have 

 for the outside of the leaf close to the seat of excitation 0*13, and for 

 the opposite side 0-24, which gives O'll instead of 0-18 as the time 

 required for transmission. In one instance, indeed, we observed by 

 repeated careful measurements as short a period as 0-06 under normal 

 circumstances. In the experiments to be mentioned in the next section, 

 when the leaves were artificially warmed, the delay was similarly abbre- 

 viated. This subject requires further investigation *. 



* It is to be remembered that the measurements were not made in the hothouse, 

 but in an ordinary room. At the time they were made we were not aware of the 

 remarkable influence of temperature. 



