350 MOTION TN ANIMALS AND PLANTS. 



variation of the heart and of muscle, respective-ly, provided that we 

 bear in mind that the one is a response to a short continuous stimula- 

 tion, the other to an instantaneous one. 



DION^A. 



My last example of motion and its accompanying electrical phe- 

 nomena I will take from the plant. As everyone knows, there are 

 certain parts of some of the higher plants which respond to stimulation 

 like the motor organs of animals. These instances have been regarded 

 as indications of the close relationship which exists between plants and 

 animals as regards their elementary physiology. The subject attracted 

 the attention of Mr. Darwin in relation to certain insectivorous plants, 

 and it was at his suggestion that the observations to which I am now 

 about briefly to refer were made. The electrical changes can be most 

 easily studied, and appear in the most striking way, in the leaf of 

 Diongea. The leading-off contacts are applied to the opposite surfaces 

 of one lobe of the leaf. In the resting state the one surface is found 

 to be positive to the other. At a certain moment a hair on one lobe 

 some 10 or 12 millimeters away from the place under investigation is 

 touched by a camel-hair pencil or excited by an induction current. 

 The surface which was before positive becomes less so, and the curve 

 described resembles, as you see, the monophasic heart curve. 



It is not necessary on the present occasion to do more than refer to 

 this typical experiment, b}^ which it was shown for the first time that 

 the migration of liquid, and consequent sudden closure of the lobes on 

 excitation, is accompanied by an electrical change analogous to that in 

 contracting muscle, and that in the leaf this is propagated at a rate 

 var^nng with temperature. Although the experiment is one of extreme 

 simplicit}^ the method of investigation has not, so far as I know, been 

 pursued by an}^ plant physiologist. The criticisms which were bestowed 

 on it by animal physiologists I was able to answer in my second com- 

 munication to the Royal Society, and have now the satisfaction to find 

 that the experimental data set forth in that paper are given in full in 

 Biedermann's important treatise on Electro-Physiology. 



I have now, though in a very incomplete way, described the phenom- 

 ena bearing on my subject, so far as I have been able to observe 

 them. May I be permitted to submit to you the indications which 

 the}^ seem to me to afford? 



In striated nmscle, the primary effect of every excitation, is a process 

 of oxidation having its seat at the excited part. It may be surmised 

 that this consists of two stages, namely, liberation of previously intra- 

 molecular oxygen and actual oxidation. . In a single element of 

 muscular structure the duration of this process, when induced by an 

 instantaneous stimulus, must be exceedingly short, and corresponds 



