March 3, 1887] 



NA TURE 



429 



prolecleil the Slate against any dangerous accumulation of elec- 

 tricity. But Prof. Milne showed that the laying down of rails 

 in Japan had no such effect, lie thought the electric pheno- 

 mena which sometimes attended earthquakes were their conse- 

 quences, not their causes, lie had himself experimented with 

 dynamite placed in a hole ; an earth-plate was fixed about thirty 

 yards away from the dynamite, and from it a wire was carried 

 some distance to another earth-plate. When the dynamite charge 

 was exploded there was certainly a current produced, as was 

 indicated by a strong deflection of a galvanometer-needle at the 

 end of the wire. He attributed this to chemical action. When 

 the ground was shaken there was always a greater or less action 

 by incease or decrease of pressure in connection with the earth- 

 plate. Earth currents unquestionably accompany earthquakes, 

 but, as has been said, they appear to be the consequences, not 

 the causes, of the latter. Next came the chemical theories, 

 which were very strong in Europe up to the beginning of the 

 present century. It was imagined that underground there were 

 various substances, such as sulphur, nitre, vitriol, which, by 

 their action on each other, resulted in violent changes, giving 

 rise to vapour, the sudden production of which, in certain cases, 

 would shake the ground. It was only in 1760 that Dr. Mitchell, 

 who wrote a good deal on the subject, first threw out the theory 

 that earthquakes were connected in some way with volcanoes, 

 because they were most frequent in volcanic countries. He 

 observed that large quantities of steam were given oft" from vol- 

 canoes, and came to the conclusion that an earthquake was 

 produced at the time that an attempt was made to form a vol- 

 cano, that steam got in between certain strata, and, as it ran 

 between them, caused pulsations. Prof. Rogers, about the same 

 lime, in North .-Vmerica, endeavoured to show that it was not 

 steam, but really lava, that ran along underneath the ground, 

 causing it to rise and fall, thus producing an earthquake. Prof. 

 Milne haWng thus dealt with unscientific and r^wa^'scientific 

 theories, passed on to those of modern science. It is unneces- 

 sary here to follow him into this portion of his subject, although it 

 occupied the main part of the lecture. 



ON THE EFFECT OF CERTAIN STIMULI ON 



VEGETABLE TISSUES'- 

 'T'HE object of our paper is to describe the behaviour of 

 turgescent pith when pl.aced in water and treated with 

 certain reagents. If from a growing shoot the external tissues 

 be removed, a well-known result is seen : the pith suddenly 

 lengthens, becoming longer than the specimen was at first. This 

 experiment shows that turgescent pith is normally in a compressed 

 condition — it is always trying to get longer — and when it is freed 

 from the coercion of the unyielding external tissues, it at once 

 does become longer. This tendency to become longer is further 

 manifested by aliening turgescent pith to remain in damp air, or 

 in water, for some time, when a great increase in length takes 

 place. In such a piece of pith we have the essential, active factor 

 in growth, freed from interference, and at liberty to perform its 

 function rapidly and freely. The tendency in turgescent pith to 

 get longer is the very power which calls forth that increase in 

 length which we call growth ; so that in studying turgescent pith 

 wc are studying the active agent in the production of growth. 

 We do not suppose that our results are necessarily directly ap- 

 plicable to normal growth," but we think that they have a 

 bearing on normal growth sufficiently close to give interest to our 

 experiments. 



The pith,' after being cut into pieces about 6 inches in length 

 and i inch in thickness, was ready for use. The lower end of 

 the pith was fixed to a hook at the bottom of a narrow jar, the 

 upper end was attached by a silk thread to the short arm of an 

 auxanometer lever. The jar was then filled with water, and as 

 the pith elongates the short arm of the lever ascends and the 

 long arm rapidly descends. Its movement, read off on a milli- 

 metre scale, gives an index of the rate of " growth " of the pith. 

 The lengthening of the pith is, in fact, observed like the normal 

 growth of a pl.ant, the only difference being that the "growth " 

 of the pith is so rapid that the descent of the long arm is clearly 

 visible to the naked eye and is correspondingly easy to measure. 

 It is most striking to see the index travelling down thus quickly 



' Abstract of a P.ipcr by Anrui B.itcson (Xewnham College) and Francis 

 Darwin (Cambridge), read before the Linnean Society, January 20, 1887. 



* For the sake of convenience we shall nevertheless use the word 

 "erowih " to mean the elongation of the pith under observation. 



3 Sunfljwcr and Jerusalem Artichoke.} 



and traversing (it may be) 10 mm. (S inch) in a minute. W'e 

 used a stop-watch to determine the time in which the point of 

 the long arm of the lever travelled over a certain distance, and 

 we could thus estimate the changes in the rate of growth from 

 minute to minute. 



The first thing needful to know is the ordinary course of 

 growth of the pith in water. It was found that an interesting 

 phenomenon — an apparent grand piriod — takes place. That is 

 to say, the growth is at first slow, then more rapid, and ultimately 

 becomes slow again, the whole period taking perhaps twenty 

 minutes to complete. This is precisely the series of changes 

 which a growing organ exhibits in the course of days instead of 

 minutes. We do not suppose that our grand period is necessarily 

 of a kindred nature to the grand period of normal growth. For 

 we are aware that purely mechanical processes, such as the 

 moistening of a hygroscopic awn, exhibit the same thing — 

 the awn at first untwists slowly, then more quickly, and then 

 again slowly. But the knowledge of the fact is of great import- 

 ance to us, since unless we know the normal course of growth 

 we cannot study the eftect of reagents. 



Warmth. — Before going on to consider the action of reagents, 

 we will say a few words as to the stimulation caused by an 

 increase in the surrounding temperature. If the water in the 

 jar is gradually warmed, the growth of the pith increases in 

 speed in the most striking manner. The increase is fairly steady 

 from, say, 17° C. to about 35°, the rate at this latter tempera- 

 ture being perhaps four times as high as it was at first. It then 

 usually becomes irregular, with some diminution ; and, just 

 before a temperature is reached which kills the tissues, a sudden 

 and rapid fall in the rate of growth sets in. This we found 

 usually to occur at about 55" C. This is, no doubt, an unusually 

 high temperature, but not higher than plants are known to be 

 able to survive. 



The chief interest in these temperature experiments is this : 

 they show that the phenomena we are considering is a truly vital 

 one. We have always been on our guard in this matter, and 

 have wished to make certain that the observed phenomena are 

 not in some mysterious way mechanical, instead of, as we 

 believe, the response of living tissues as living tissues. There- 

 fore, when we find that heat has a normal effect on our material, 

 we are encouraged to believe that our other results — to which 

 we now pass on — are also vital phenomena. 



Alcohol. — The pith was attached to the auxanometer, and the 

 jar filled with water. As soon as the rate of growth was found 

 to be steadily diminishing, a small quantity of alcohol was added. 

 The result was an immediate and striking increase in the rate of 

 growth. For instance, when 2 per cent, of spirit was added, 

 the growth was accelerated within two minutes by 50 per cent. 



The result is temporary, so that in the course of another two 

 minules the rate of growth sinks to what it was before stimu- 

 lation. Similar results were obtained with ether, and here the 

 pith was allowed to grow in damp air, and was subjected to ether 

 in the form of vapour. When the vapour was present in the 

 proportion of 0'27 per cent., the acceleration was 56 per cent. ; 

 with 0'4 per cent., the acceleration was 100 per cent. Here, as 

 in the case of alcohol, the result was temporary, the rate falling 

 in a few minutes to what it was before stimulation. 



When the ether amounts to 3 per cent, of the atmosphere, 

 the pith is killed, and shows no increase, but, on the contrary, 

 a decrease ' in length. Elfving h,is shown that ether has a 

 stimulating effect on respiration, and on the sensitiveness of 

 swarm-spores to light. He also tested its effect on the growth 

 of phycomyces. His results differ from ours, inasmuch as he 

 found no stimulating effect : the ether produced either no 

 effect whatever, or else it retarded, or even stopped, growth. 



Ammonia. — We employed the Liquor Ammoni(V fortior of 

 the " British Pharmacopoeia " for the preparation of our solu- 

 tions, and we found that various strengths ranging between 0'5 

 and 2 '4 per cent, produced acceleration of growth. Here 

 again, as with ether and alcohol, the acceleration was very 

 temporary. 



Acids. — As a rule, acids produced no acceleration, but caused 

 either retardation, or flaccidity and death. Thus, for instance, 

 acetic acid (o'S and i per cent.) produced retardation ; 5-4 per 

 cent, produced death. 



Hydrocyanic Acid did not cause flaccidity such as we 

 have described in the case of acetic acid. The action of this 

 reagent is comparable rather to that of alcohol, but is not 



' Ihis contract'on is sim. ly a symptom of flaccidity, and usually of 

 death. 



