August 10, 1882] 



NA TURE 



353 



water-transformations much more important than those on our 

 globe. There are also papers on Venus and her satellite, the 

 tides in the Mediterranean, the heavens in August, &c. 



A CURIOUS and little-known experiment, showing the resist- 

 ance of the air in guns, is described by Prof. Daniel Colladon, 

 of Geneva, in a recent letter to M. Melsens [Bull. B,/g. .lead. 

 No. 6). He was long in the habit of showing it to his classes. 

 It resembles a feat that was sometimes performed by soldiers 

 with the old Swiss carbines. M. Colladon fully charged with 

 compressed air the hollow iron breech of an air-gun, serving as 

 reservoir. Having screwed up the gun, he introduced a round 

 lead ball, running freely, but nearly filling the bore ; then, 

 placing the gun vertical, he seized the upper end and pressed his 

 thumb vigorously on the mouth. The gun was then " fired " by 

 at ; the thumb remained in position, and the ball was 

 heard to fall back in the bore. Thereupon, after recharging the 

 breech and with the same ball, he shot the latter at a pine board 

 about *4 in. thick, or a pane of glass, and it pas.-ed through. 

 The experiment, M. Colladon says, is without danger, if the 

 operator is sure of the strength of his thumb, if the gun is more 

 than 32 in. long, and if the ball is spherical and nearly fills the 

 gun (in which it must act like a piston). The least uncertainty 

 in the very vigorous pressure of the thumb, and hermetic closure 

 of the gun, may entail serious injury to the thumb. While 

 M. Colladon has repeated the experiment twenty or thirty times, 

 without the least inconvenience either from shock or heat, a 

 trial of it is perhaps hardly to be recommended. 



The additions to the Zoological Society's Gardens during the 

 past week include a Common Raccoon (Procyon lolor) from 

 North America, presented by Mr. Mark Vice; a Pa -serine Owl 

 (Glaucidium passe; inum), European, presented by Miss Maud 

 Howard; six Common Guillemots (Uria troile), European, pre- 

 sented by Sir Hugh Dalrymple, Bart. ; an Allen's Porphyrio 

 (Porpliyrio alUni), captured at sea, presented by Master J. 

 Kennedy ; forty Restless Cavies (Cavia caprcra), British, pre- 

 sented by H. R.H. the Prince of Wales, K.G. ; a Four-rayed 

 Snake (Elaphis quaterradiatus), South European, presented by 

 Capt. Adams ; a Smooth Snake (Corone/la tan/is), British, pre- 

 sented by Mr. W. Penney ; an Egyptian Cobra (Naia haje) from 

 South Africa, presented by Mr. Eustace Pillans ; a Common 

 Viper (I'ipera berus), British, presented by Mr. H. J. Benwell; 

 a Lesser White-nosed Monkey (Cercopithecus petaurisla) from 

 West Africa, a Grey Ichneumon (Herpestcs griseus) from India, 

 a Goffin's Cockatoo (Cacalua gojffini) from Queensland, a White- 

 headed Sea Eagle (Haliaetus leucoeephaius) from North America, 

 a Chequered Elaps (E/aps lemniscalus) from Brazil, deposited ; 

 three Black Lemurs (Lemur macaco 6 6 9 ), a White-fronted 

 Lemur (Lemur albifrons 6 ) a Red-fronted Lemur (Ltmur rufi- 

 frons i ) from Madagascar, a Cape Hyrax (Hyrax capensis) 

 from South Africa, a Westerman's Cassowary (Casuariits wester- 

 maniii) from New Guinea, two Pileated Jays (Cyanocorax 

 pihalus) from La Plata, two White-faced Tree Ducks (Dendro- 

 eygua liduata), two Rufous Tinamous (Rhynchctus rufescens) 

 from Brazil, two Tataupa Tinamous (Crypturus tataupa) from 

 South America, an Argentine Tortoise (Testtido argentina) from 

 the Argentine Republic, two Common Chameleons (Ckamalcon 

 ■vulgaris) from North Africa, two Aldrovandi's Lizards (Plestio- 

 don auratus) from North-West Africa, purchased ; two Mucas 5 in 

 Snakes (Tropidonotus fasciatus), born in the Gardens. 



THE EXCITABILITY OF PLANTS 1 

 TT will be in the recollection of many who are present this 

 x evening that in February of last year I had the honour of 

 delivering a Friday evening discourse on a subject which included 

 that which has been announced for to-night. In that lecture I 



1 Lecture delivered at the Royal Institution June 9, 18S2, by Prof. Burdorr 

 Sanderson, F.R.S. 



had hoped to present to you a comprehensive view of the ex- 

 citatory motions both of plants and of animals ; that is, of those 

 motions which they perform in response to transitory impressions 

 received by them from outside. I was desirous that the state- 

 ments that I made to you with reference to animal excitability 

 should be as fully as possible illustrated by experiments, in the 

 carrying out of which much more time was lost than I had 

 reckoned for ; so that I was unable even to enter on the second 

 part of my subject. The time at my disposal will not permit me 

 to summarise my last lecture, however advantageous it might be 

 to do so. I must content myself with recalling your attention to 

 one or two fundamental points. 



U nder the term excitability are comprised all cases in which some 

 definite change in the behaviour of a living structure, whether it 

 be a whole animal or a part, constantly arises as the result of 

 some transitory external influence. But for the purpose in view, 

 those cases only were included (typical of the rest) in which some 

 sort of muscular motion is performed in response to an excitation 

 or stimulus. The effect of such excitation we call the excita- 

 tory process, and we say, as the result of observation, that it 

 consists of two phases or stages — namely, the phase of latency, 

 and the phase of visible effect. Thee were illustrated in the last 

 lecture by a series of experiments in which the excitable tissue of 

 the heart of the frog was used. It was first shown with refer- 

 ence to this tissue that when it is touched (that is excited) with the 

 tip of a glass rod, it undergoes a definite change of form, at the 

 same time doing mechanical work at the expense of material 

 contained in, but not forming part of, its own substance ; 

 secondly, that this mechanical effect did not begin until the lapse 

 of an easily measurable period after the excitation, ; it was then 

 pointed out that the interval of time between the prick and the 

 visible or mechanical effect — the change of form, or contraction 

 of the contractile substance — was one during w hich, though no 

 visible change occurred in the excited part, molecular changes 

 must certainly be in progress, and that these were accompanied 

 by electrical disturbance. 



To illustrate this, I demonstrated to you that the electrical 

 change which in all cases accompanies excitation, precedes the 

 mechanical one in time. You will remember that by means of 

 the electric light the outline of the muscle to be excited and 

 the image of the galvanometer mirror were projected on the 

 screen, and that we were able to observe that when the muscle 

 was pricked, the electrical disturbance had time to produce a 

 deflection of the magnet which was visible on the screen before 

 the muscle contracted. 



It was further shown that an excitatory effect analogous to 

 that which in muscle constitutes the first phase is produced in 

 nerve, that in both the process of excitation is capable of 

 being propagated in the same sort of way that an explosion 

 is propagated in a train of gunpowder, and, finally, that tire 

 existence in nerve of this endowment is the instrumentality by 

 which, in the human body, the will is able to influence and 

 govern all the rest, and to receive influences from outside. 



To-night we shall occupy ourselves exclusively with plants. I 

 shall endeavour to show not only that they possess the wonderful 

 property of excitability by which one part is able to influence 

 another part at a distance, but that there is reason for believing 

 that the excitability they possess is essentially of the same nature 

 as that of animal tissue. And now, without further preface, I 

 propose to enter on my subject by first giving you a short account 

 of some of the most instructive instances of excitable plants. 



The number of plants which exhibit what is often called 

 irritability is very considerable. I will not weary you with even 

 enumerating them. You will see from the table that they are 

 distributed among a number of natural orders, so that one might 

 be inclined to suppose that in this respect no relation could be 

 traced between the physiological endowments and the morpho- 

 logical characters of a plan - . That it is not so we have abun- 

 dant evidence. Thus in the same genus we may find all the speeies 

 excitable, though not in the same degree. The extreme sen- 

 sitiveness of the Chine-e Oxalis, formerly called Biophytum 

 sensilivum, because it was supposed to be particularly alive, 

 appears in a less degree, but equally distinctly in our own wood 

 sorrel, as well as in the Tree Oxalis of Bengal — the Carambola, 1 

 which is described in an interesting letter addres-ed by Dr. 

 Robert Bruce to Sir Jos. Banks, and published in the Philo- 

 sophical Transactions. Again, in the same order, as, for example, 

 among composite plants, we may have the Thistles, Knap- 



1 An account of the sensitive quality of the tree'Averrhoa Carambola. By 

 Robert Bruce, M.D. Phil Trans., vol- lxxv. p. 356 



