xii Obituary Notices of Fellows deceased. 



lay in the circumstance that it was successively developed in all parts of the 

 leaf lobes, indicating the propagation of some active cellular change from the 

 seat of the stimulus to more remote regions. 



In 1877 an account of this discovery, together with the experimental 

 determination of the time relations of this electrical response, formed the 

 subject of the Croonian Lecture of that year, the title of the lecture being 

 " The Mechanical Effects and the Electrical Disturbance Consequent on 

 Excitation of the Leaf of Dioncea muscipula." Five years later, in 1882, a 

 more extended and detailed account of the phenomena was published in the 

 'Philosophical Transactions,' entitled "The Electromotive Properties of the 

 Leaf of Dionsea in the Excited and Unexcited States." From the careful 

 analysis which he had made of his experimental observations, he concluded 

 that the excitatory disturbance, "by the mode of its origin, the suddenness of 

 its incidence and the rapidity of its propagation, is distinguished from every 

 other phenomenon except the corresponding process in the excitable tissues 

 of animals." "In the one case as in the other," he continues, "we must 

 regard the electrical change as a visible sign of an unknown molecular 

 process." The actual mechanical displacement he agreed with Pfeffer in 

 considering as probably related to " the diminution of the turgor or water- 

 charge of the protoplasm of the excitable cells." The experimental evidence 

 which he now brought forward appeared to indicate two possible sources of 

 electromotive change ; there was shown to be an initial or primary change, 

 sudden in its development, brief in its duration, and always of the same 

 general type ; this he regarded as the electrolytic indication of the peculiar 

 molecular alteration in the plant cells which constitutes the excitatory state ; 

 it was succeeded by a second change of longer duration and often of different 

 sign, which was attended by a prolonged residuum or after effect ; this he 

 regarded as associated with diminished turgor and consequent displacement 

 of water. It was only by accurate methods of recording that he was enabled 

 to discriminate between the primary and secondary effects and to show that 

 as regards the primary or initial change the active excitatory state is 

 fundamentally the same, whether it occurs in these vegetable cells or in 

 excitable animal tissues. 



A third paper upon the electromotive properties of the leaf of Dionsea 

 appeared in the ' Philosophical Transactions' of 1888. This paper included 

 a number of experimental observations as to the behaviour of what he 

 termed " modified leaves " ; the observations were made in Oxford, and 

 involved the use of a special double rheotome ; the capillary electrometer 

 was also employed, and photographic records of the excitatory electrical 

 changes are given in the paper. 



The observations show several interesting facts, but the chief points 

 brought out refer to the so-called "modification," which is produced in 

 a leaf when it is subjected to the flow of even a weak voltaic current. The 

 modification reveals itself as a permanent alteration in the amount, and even 

 the sign of the electrical state of the inactive leaf-surface. It is localised to 



