Vol. Xlir. Xo. 322 



THE AGRICULTURAL XEWS. 



RE-ACTION TO STIMULUS. 



PLANT SENSIBILITY AND ITS 

 REVELATION. 



F<ir many years it has been an o]jeii question wlietlier 

 tliere is any fundamental unity in the rcspon.se of plants and 

 animals to external stimuli. In the case of certain plants it 

 lias been known for many years that these are able to respond 

 in a marked degree to various forms nf treatment but as to 

 whether it is rhythniatic and whether in degree it holds gond 

 for all plants had not l>een definitely establishal until Pro- 

 fessor J. (_'. Bose investigated the subje<-t a few years agf). 



In Xfitiire for July 2-3, 1!M4, there appears an article 

 t-ntitled I'laut Autographs and their lievelation, in which the 

 ingenious apparatus used by Professor Hose for obtaining an 

 answer to the various ipiestions regarding rhythmatic sensi- 

 bility, and the results which had been obtained in the investi- 

 gation are fully de.scribed and illustrated. 



15y the invention of different types of recorders it has 

 Leen possible to make the ])laut itself write an au.swering 

 script to a testing stinudus. First attempts to obtain these 

 :inswers were maile with ;i comparatively simple recorder and 

 in priniiple the method is as follows. In the case of the 

 ^Mimosa plant, which has been the jirincipal subject of inves- 

 tigation, an electric cm-rent is pas.sed through the plant by 

 the tendrils, the leaf being attached by thread to one arm of 

 a lever to which i» fixed a writing index that traces on 

 .smoked glass the responsive fall and recovery of the leaf 

 induced liy the electric shock. In attaining the actual record 

 of this movement in plants many serious difticidties are 

 encountered, the principal one being that the movements 

 which may be induced will not always overcome the friction 

 of the apparatus. This difticidty was overcome liy making 

 an intermittent instead f)f a continuolLS recorder. The 

 [Kissibility of this lay in rendering the writer tremulous, 

 this being accomplished by an invention depending on 

 the phenomenon of re.sonance. Hxiiressed in the simplest 

 terms, the index writer and a reed are tuned to the same |)itch. 

 In aic-ordaiice with the well-known law of acoustics if a note 

 is sounded on the reed, the index will vibiate in sympathy and 

 in conseipience will deliver on the recording plate of glass 

 a siu'cession of taps many hundred time.s a second. By 

 inean.s of this it is not only possiljle to get rid of the error 

 <lue to friction, but make the record itself measure time as 

 short as may be desired. The extraordinary delicacy of the 

 instrument may be understood when by its means it may be 

 possible to record a time interval as short as the thr>usandtli 

 part of the duration of a single beat of the heart. 



The first subject which received investigation was the 

 so-called 'sleep <jf plants.' In order to find out whether 

 Mimosa, a plant which exhibits sleep movement.s, shows 

 <liurnal variations of sensibility, a specimen was made to 

 answer to uniform ijuestioniug shocks repeated every hour of 

 the day or night. The amplitude of the answering twitch 

 gave a measure of the wakefulness of the plant during 

 twenty-four hours. The results obtained were quite unex- 

 pected and are described by Professor Bose in the following 

 words: 'The plant is found to keep up very late and fall 

 asleep oidy at the early hours of the morning. It makes up 

 for its late hours liy gradually waking up by noon. It then 

 remains in a condition of uniform s-iisibility all the afternoon. 

 This period of uniformity is chosen for investigations on the 

 fleet of changed external conditions on excitability.' 



-\s regards the effect of air, food and drugs, it. has been 

 demonstrated by means of plant autograpLs that the plant 

 may lie suffocated if the air contain.? a large percentage of 

 carliouic acid gas and the autograph pub!i.shed in the article 

 under review clearly shows what Professor Bose ells the -gasp 

 of relief when fresh air is introduced. Only in the pre.sence 

 of >unlight is this effect modified by photosynthesis. lu eon- 

 tiast to the effect of carbonic acid, ozone reiiders the plant 

 highly excitable. Sulphuretted ' hydrogen, even in small 

 quantities, is very fatal, and aleoliol give- r''-.i *• 'a ludicrous 

 unsteadiness of gait.' 



Interesting though the.se re.sults u.'iuoubt.idly are, it Ls 

 even more instructive to know that it has been established 

 that they are common to all plants. Moreover the autograph.s 

 olitained show that there is a latent pericid between the 

 application of the stimulus and the first sign of respo!..se 

 which is a characteristic phenomenon in regard to the resptn'se 

 to stimuli in men and animals. 



The determination of the speed of impulse in plants ha,s 

 received attention, and it has been shown that the true time for 

 the excitation to travel through a distance of 3C> milliirictre.s 

 in a plant is L5 .seconds, the velocity being 20 millimetre)? 

 per second. The velocity of nervous impulse in th* plant is 

 slower than those of higher, but quicker than thjse of lower 

 animals. The speed of the impulse is; however, subject to varia- 

 tion under ditferent conditions. One .sig:iificaiit result thtit came 

 out was that, while a plant carefully protected under glas-s 

 from outside blows looks .sleek and fi.jv.rishing, yet as a com- 

 plete and perfect organism it proved to be a failure. Its con- 

 ducting power was found to be paralyzed. But by the con- 

 tinued application ■if stimuli its nervous impulse- bT.tJns 

 \ery much quickened after a time. 



It is a very interesting fact that temperature Iias been 

 found to alfect the rate of nervous transmission. In the case 

 of the plant it seems that the velocity is doubled by a rise of 

 temperature through 9°C When a portion of the 'lor-ducting 

 petiole if subjected to cold, the .speed of conductioi; i= retard- 

 ed. Kxcessive cold temporarilj' abolishes the sonducting 

 power. It is a suggestive fact that the normal noaditions of 

 a plant can be restored by subjecting the sterilized portioL of 

 the plant to a measure of moderate doses of electric shock. 



As well as the various phenomena already described as 

 having been shown to exist. Professor Bose claims that by 

 means of an oscilating recorder or 'pulse record', he can sLuw 

 the existence of spontaneous pulsation in plants simlLr to 

 that exemplified in animals by the beating of the heart. For 

 instance the leaves of a plant D. gy anx have been shown to 

 grow in a state of perpetual vibration. As a contimia.tion 

 of this discovery remarkable parallelisms were found to exist 

 in regard to the etfe<-t of anesthetics, all of which tend to 

 show that there is a strong relationshir between the sensi- 

 tiveness of plants anil that of ainmals. 



Lastly the methods of investigation oix which liic results 

 outlined above are based have been used siiccessfuUj' to 

 measure with great accuracy the rate of the growth in the 

 |)lant. Although by calculation it can be computed that it 

 «(iuld take an average plant 200 years to coyer the short 

 distance of a mile, the extreme slowness of the development 

 is a serious drawback to an accurate scientific determination. 

 Professor Bose, however, claims that difficulties have been 

 overi'ome by his invention of a cresi-ograph which record.s 

 the absolute rate (if growth in a time so short as a single 

 beat iif the pendulum. The actual rate oi growth and its 

 variation under the action of nutrients, vaiious electrical and 

 other forms of stimuli are thus recorded in the coiir.?e oi 

 a few minutes. The great impoj'tance of this methnd ni_ 

 investigation in agriculture is sufficiently ouvioLUS. 



