6^0 LECTURE XXXVII. 



to contact or shocks are the leaves of Dionaa viuscipula, already described 

 in Lecture XXIV : as there stated, the laminae clap their two halves together 

 with lightning-like rapidity when one of the six hairs of the upper side is roughly 

 touched. From -Batalin's detailed researches ^ it may be concluded that in the 

 case of Dioncea also it depends essentially upon similar changes in the tissue 

 of the mid-rib, and in part of the lamina, as in Mimosa ; but several new points 

 with respect to the relative arrangement of the active parts necessarily come in, and 

 a lengthy description would be necessary to give the reader a really clear idea 

 of the mechanism of the leaves of Dionaa. It suffices for the purpose of this book 

 to have shown in one example what is most important concerning the phenomena 

 of irritability produced by contact and vibration. 



I will here refer to one point only by the way. Burdon- Sanderson, by 

 employing the well-known very sensitive electrical apparatus used by animal physio- 

 logists for the detection of electrical changes in nerves and muscles, found that, 

 on stimulation, electric currents arise in the leaves of Dionaa, and considering 

 the general ignorance which prevails as to botanical matters it can scarcely be 

 wondered at if the conclusion was drawn from these observations that something 

 of the nature of animal nerves exists in the leaves of Dionaa, as appeared more- 

 over to accord excellently with the insectivorous propensities of these plants. Our 

 ideas of the irritability of plants, explained with so much trouble and labour, will one 

 day be applied to the utterly obscure views as to the so-called negative variation 

 in animal nerves. Without entering more in detail into the criticism of the 

 matter, it may simply be mentioned that at my suggestion, and in my laboratory. 

 Dr. Kunkel '', well versed in the technicalities of electrical investigations, established 

 the fact that each movement of the water in the tissues of a plant induces feeble 

 electrical currents in it. In the case of a slight bending of a shoot-axis or of 

 a leaf-stalk, which must entail movement of the water in the tissues, electrical 

 disturbances can at once be detected with delicate instruments. Since now, as 

 has been shown above, every movement of irritation of the leaves is connected with 

 what amounts to a very considerable displacement of water in the tissues, this 

 also must produce electrical disturbances, and conversely, it is also obvious that 

 electric disturbances acting from without must act as stimuh to movement. These 

 have been longest known in Mimosa. In any case, then, we have no necessity to 

 refer to the physiology of nerves in order to obtain greater clearness as to the 

 phenomena of irritabihty in plants; it will, perhaps, on the contrary eventually result 

 that we shall obtain from the processes of irritability in plants data for the explana- 

 tion of the physiology of nerves, and this, although it is as yet a very distant hope, 

 gives a special attraction to the study of the irritable phenomena of plants. I shall 

 therefore invite the reader to consider with me, somewhat in detail, the more im- 

 portant phenomena of irritability in the stamens of the Cynarese.. 



The Cynarese are a subdivision of the great family of Composite, in which 



' Batalin, ' Mechanik der Bewegungen lier insektenfressenden Pflanzen.^ Flora, 1877 (pp. 33, 

 &c.), where Drosera and DiontBa are treated with especial care. 



^ Knnkel, ' Uber^ ekktromotorische Wirkungen an unverUtzten Ubenden Pflaneentheilen! in Arb. 

 des hot, Inst. Wiirzbg.,' 1878, B. II (p. i) ; and further, • Uber einige Eigenthumlichkeiten des ekk- 

 Irischen LeitungsvermSgens lebender Pflanzentheiles,' 1879 (ibid., p. 333). 



