Life Movements in Plants

I have recently been successful in devising an ideal method of magnification without contact. The movement of the lever of the Crescograph upsets a very delicately balanced magnetic system. The indicator is a reflected spot of light from a mirror carried by the deflected magnet. Taking a single lever with the lengths of two arms 125 min. and 2*5 mm. respectively we obtain a magnification of 50 times. The magnetic system gives a further magnification^ of 20,000 the total magnification being thus a million times. This was verified by moving by means of a micrometer screw the short arm of ■* the lever through 0*005 mm. The resulting deflection of the spot of light at a distance of 4 metres was found to be 5,000 mm., or a million times the movement of the short arm. It is not difficult to produce a further magnification of 50 times by attaching a second lever to the first. The total magnifica¬ tion would in this case be 50 million times.

A concrete idea of this will be obtained when we realise that by the Magnetic Crescograph a magnification can be obtained which is about 50,000 times greater than that produced by the highest power of a microscope. This order of magnification would lengthen a wave of sodium light to about 3,000 cm. I am not aware of any existing method by which it is possible to secure an amplification of this order of magnitude. The application of this will undoubtedly be of great help in many physical investiga¬ tions, some of which I hope to complete in the near future.

Such an enormous magnification caunpt be employed in ordinary investigations on growth, for the moving spot. of light indicating rate of growth, passes like a flash across the screen. But it is of signal service in my in-.,, vestigations on growth by the Method of Balance, to be described in a future Paper, The principle of. this method consists in making the spot of light, which is moving in response to growth, stationary, by subjecting the plant to a compensating movement, downwards. The slightest variation caused by an external agent would make the spot of light move either to the right or to the left, according to the stimulating or depressing character of the agent It will be understood, how extremely sensitive this method is for detection of the most minute variation in .the nor¬ mal rate of growth.

Before proceeding with accounts of further investiga¬ tions, I shall describe a form of Magnetic Crescograph with which I have been able to give before a large audience demonstration of a striking character on various phenomena of growth. The magnification obtained was so^great that I had to take some trouble in reducing it. This was accomplished by the employment of a single, instead "of a compound system of two levers. The re¬ flected spot of light was thrown on a screen placed at a distance of 4 metres, and this gave a magnification of a million times; it is, obvious that an increase of the distance of the screen to 8 , 'metres would have given a magnification of 2 million times. . As it was, even the lower magnifica- . Idon was far too great for use with quick growing plants ilike Kywor . I, therefore, employed the slower growing flower bud of Crinum. _ It will be seen from Table X that the normal rate of growth of the lily is of the order of 0*0006 mm. per second. The normal excursion of the spot of light reflected from the Crescograph exhibiting

growth was found to be 3 metres in five seconds or GO cm. per second. This is a million times the actual rate of growth of the Crinum bud. As it is easy to measure 5 mm. in the scale, it will be seen that with the Demonstration Creseograph it is possible to detect the growth of a plant for a period shorter than a hundredth part of a second. Experiment -57.— A scale 3 metres long divided into cm. is placed against the screen. A metronome beating half seconds is started at the moment when the spot of light transits across the zero division ; the number of beats is counted till the index traverses the 300 cm.

• At the normal temperature of the room (30 C.), the index” traversed 300 cm. in live seconds. The plant chamber was next cooled to 26 ,J C. by the blowing in of cooled water vapour ; the time taken by the spot of light to traverse the scale was now 20 seconds, i.e., the growth- rate was depressed to a fourth. Under continuous lower¬ ing of temperature the growth-rate became slowed down till at 21°C. there was an arrest of growth. Warm vapour was next iutro iuced, gradually raising the tempera¬ ture of the chamber to 35-C. The spot of light now rushed across the scale in a second and a half, i.e., the growth was enhanced to more than three times the normal rate. The entire series of the above experiments, on the effect of temperature on growth, was thus complet¬ ed in the course of 15 minutes.

A description is given of the High Magnification breseograph, which enables an automatic record of growth magnified ten thousand times. The absolute rate of growth can be easily determined from the data given in the A magnification of a million times is obtained by the employment of Magnetic amplification. An increment cf growth so miuute as a millionth part of a mm. or 0-00000004 inch may thus be detected. It is also possi¬ ble to detect the growth of a plant for a period shorter than a hundredth part of a second.

The influence of external . conditions on variation of rate of growth is obtained by two methods of record. In STATIONARY METHOD, the increase or diminution of the' distance between successive dots representing magnified rate of growth, demonstrates the stimulating or depressing nature of the changed condition. In the second, or MOVING plate METHOD, a curve is ■obtained, the ordinate representing growth elongation, and the abscissa, time. A stimulating agent causes an upward flexure of the normal curve; a depressing agent, on the other hand, lessens the slope of the curve.

The action of external stimulus induces a variation of ,theN rate of growth, the time relations of which are found from the automatic record of the growth. The latent period is shortened with the intensity of the stimulus. A responsive variation of growth is induced by an intensity of stimulus which is below human perception. It is often possible to obtain record of the pulsatory nature of growth-elongation. Thus with the growing peduncle of Zephyranthes, the growth pulse commences with a sudden elongation, the maximum rate being 0-0004 mm. per second. The pulse exhausts itself in 15 seconds, after which there is a ' partial recovery in course of 13 seconds, the period of complete pulse being 28 seconds. The resultant growth in each pulse is the difference be¬ tween elongation and recovery.

The Magnetic Crescograph enables demonstration of principal phenomena of growth and its variation befor^'a large audience. Accurate determination of the effect of temperature on growth presents many serious difficulties on account of numerous complicating factors. In nature, the upper part of the plant is exposed to the temperature of the air, while the root underground is at a very different temperature. Growth, we shall find, is modified to a certain extent by the ascent of sap. (See p. 189, Expt. 69.) The activity of this latter process is determined by the temperature to which the roots are subjected. The difficulty. may be removed to a certain extern by placing the plant in a thermal chamber, with arrangement for regulating the temperature of the air. The air is a bad conductor of heat, and there is some uncertainty of the interior of the “plant attaining the tem¬ perature of the surrounding air, unless the plant is long exposed to the definite and constant temperature of the plant chamber. Observation of the effects of different tempera¬ tures then becomes a prolonged process, with the possibility of vitiation . of results . by autonomous variation of growth. Reduction of the period of experiment by. rapidly raising "the temperature of the. chamber Introduces fresh difficulties; for a sadden variation of temperature often acts like .an excitatory shock. This drawback may

to some extent be obviated by ensuring a gradual change of temperature. This is by no means an easy process, for even with care the rise of temperature of the air cannot be made perfectly uniform, and any slight irregularity gives' rise to sudden fluctuations in the magnified record of'growth. Another difficulty arises from the radiation of heat-rays from the sides of the. thermal, chamber. These- rays, J shall in a different Paper show, induce a retardation of growth The effect of rise of temperature in acceleration of growth is thus antagonised by the k action of thermal .radiation. This trouble may be minimised by having the inner surface of the thermal chamber of bright polished metal, since, the radiating power of a polished surface is relatively feeble.

The contrivance which 1 employ for ensuring a gradual rise of temperature, consists of a double-walled cylindrical metallic vessel; the plant is placed in the inner chamber, the walls of which are* coated with electrically deposited silver and polished afterwards, and at the bottom of -which .there is a little water. The space between the inner and outer cylinder is filled with water, in which is immersed a coiled copper pipe. Hot water from a small boiler enters the Inlet of the coiled pipe and passes through the outlet at the lower end. The ; water in the outer cylinder is thus gradually raised by low of hot water in the coiled .pipe., The rate of flow of hot water, on which the rate of rise of temperature depends, is regulated by a stop-cock. The air of the inner chamber in which the plant is. placed, may thus be adjusted for a definite temperature. The small quantity of water in the inner chamber keeps its air in a humid condition, since dry hot air by causing dessication interferes .with-normal growth.

. Experiment &$.—High, .magnification. records are taken for ■■■ successive periods of ten seconds, lor selected temperatures,. during the particular observation. In figure 63 is given records of rate ot growth obtained with a specimen of Kysoor at certain selected tempera¬ tures. It will be seen that the rate of growth increases with the rise of temperature to an optimum, beyond which the growth-rate - undergoes a depression. In the present case the optimum temperature is in the neigh¬ bourhood of 35°C.

PJG. 63 .—-Effect of temperature on growth, and determination of optimum tem¬ perature. The method of observation that I have described above is not ideally perfect, bat the best that could be devised under the circumstances. A very troublesome complication of pulsations in growth, arises at high temperatures, which render further record extremely difficult. Growth is un¬ doubtedly a pulsatory phenomenon; but under favourable circumstances, these merge practically into a continuous average rate of elongation. At a high temperature the effect of certain disturbing factors comes into prominence. This may be due to some slight fluctuation in the temperature of the chamber, or to the effect of thermal .radiation from the side of the chamber. This disturbing influence is most noticed at about 45°C, rendering the record of growth above this point a matter of great uncertainty. It will

presently be shown that in plants immersed in water-bath growth is often found to persist even up to 57°G. The only way of removing the complication arising from thermal radiation lies in varying the temperature condition of the plant, by direct contact with water at different tem¬ peratures. This procedure will also remove uncertainty regarding the body of the plant assuming the temperature of surrounding non-conducting air. The disturbing effect of sudden variation of temperature is also obviated by a more uniform regulation of rise of temperature. The inner cylinder containing the plant is filled with water; heat from gradually warmed water in the outer cylinder is conducted across the inner cylinder made of thin copper and- raises ° the temperature of the water contained in the inner cylinder with great uniformity. A clock-hand goes round once in a minute; the experimenter, keeping his hand on the stop¬ cock, adjusts the rate of rise of water in the inner cylin¬ der, so that there is a rise, say, of one-tenth of a degree every 6 seconds or of one degree every minute. The mass of water acts as a governor, and prevents any sudden Actuations of temperature. The adoption of this parti¬ cular device eliminated the erratic changes in the rate of growth that had hitherto proved so baffling.

The elongation recorded by the Crescograph will now be made up of (1) physical expansion, (2) expansion brought about by absorption of water, and (3) the pure acceleration of growth. The disentanglement of these different elements presented many difficulties. ' I was, however, able to find oup the relative values of the first two factors in reference ,to the elongation of growth. This was done by carrying ©fit a preliminary experiment with a specimen of plant in which growth had been completed. It was raised through 20°C in temperature, records being taken both at the beginning and at the end. This was fbr obtaining a measure of the

physical change due to temperature, and also of the change brought about by absorption of water. I should state here that for the method of continuous record of growth which I contemplated, the record had to be taken for about 18 minutes. The magnification had to be lowered to 250 times to keep the record within the plate. With this magni¬ fication, the fully grown specimen did not show in the record a change even of 1 mm. in length in 18 minutes, while the growing pi ant under similar circumstances exhi¬ bited an elongation of 100 mm., or more. In records taken with low magnification, the effect of physical change is quite negligible.

The cardinal points of growth are not the same in different giants ; they are modified m the same species by the climate to which the plants are habituated ; .the results obtained in the tropics may thus be different from those obtained in colder climates. At the time of tM experiment, the prevailing temperature at Calcutta in day time was about 30°C. Temperature minimum: Experiment 59 .—For the deter¬ mination of the minimum, I took a specimen of Kysoor, and subjected it to a continuous lowering of temperature, by regular flow of ice-cold water in the outer vessel of the plant-chamber. Record was taken on a moving plate for every degree fall of temperature; growth was found to be continuously depressed, till an arrest of growth took place at 22°C (Fig. 64).

The arrested growth was feebly revived at 23 C, afteiy which with further rise of temperature there was increased acceleration. The optimum point was reached at about 34°C. In some plants the optimum is reached at about 28 0, and the rate remains constant for the next 10 degrees or mordi Fig. 54.—-Record of effect, of fall of temperature from S(PC to arrest of growth" Fig. 65.—Effect of rise of temperature from 53 3 C to 60 3 C. A sudden contraction, indicative of death-spasm, takes place, at 60 3 C.

.Temperature maximum: Experiment 60 .—For the deter¬ mination of the maximum, the temperature was raised much higher. At 55 C. growth was found to be greatly retarded with practical arrest at 58 C. At 60 G there occurred a sudden* spasmodic contraction (Fig. 65), which' I have shown elsewhere to be the spasm of death. This mechanical spasm at 60 0 is also strikingly shown by. various pulvinat- ed organs. An electric spasm of galvanometrie negativity, -and a. sudden diminution of electrical resistance also .take place at the critical temperature of 60'’G.*

I have described the immediate effect at the critical point. Long maintenance at'a temperature"" few degrees below 60 D C, will no doubt be attended witli the death of the organ. Fatigue is also found to lower the death-point. Experiment 66. — I was next desirous of devising a method by which an automatic and continuous record of the plant should. enable us to obtain a curve, which would give the rate of growth at any temperature, from the arrested growth at.the minimum to a temperature as high as 40°C- la order to eliminate -the elements of spontaneous variation, the entire record had to be completed within a reasonable length of time, say about 18 minutes for a rise of as many degrees in temperature. This gives a rate of rise of 1°G. for one minute. Separate experiments showed that at -this rat© of continuous rise of temperature there is practically no lag in the 'temperature assumed by thin specimens of plants. For observation during a limited range i use the slower rate of rise at 1°C per two minutes. But the result obtained by slower rise was found -not to differ from that obtained with one degree rise per minute. -The curve of growth is taken on a moving plate, which travels 5mm. per minute. Successive dots are made by the recording lever alV intervals of a minute during which the rise of temperature is 1°0. A Thermo-crescent Curve is thus obtained, the ordinate of which represents increment of growth, and the abscissa,' the time. As the temperature is made to rise one degree per minute, the abscissa also represents rise of temperature (Fig. 66). The vertical distance between two Successive dots thus gives incremeatof growth in one minute for 1 degree rise of temperature from T to TV If l repre¬ sents this length, t the interval of time (herb 60 sec.), and v m the magnifying power of the recorder, then the ratfe- of

It will thus be seen that, in the course of an experiment lasting about twenty minutes, data have been obtained which enable ns to determine the rates of growth through 'a wide range of temperature. We have likewise been able by the first method to make very accurate determinations of the temperature maximum and minimum. In short, by adopting the methods described, the cardinal points 'of growth and the rate of growth at any temperature, may be determined with a precision unattainable by the older methods, of averages or of prolonged observation.

Temperature induces variation in the rate of growth. In accurate, determination, of the growth, the disturbing effect of radiation of heat has not be eliminated A continuous record of growth under uniform rise* of temperature gives the Thermo-crescent curve,, from . which the rate of growth at any temperature may be deduced. Different plant-tissues exhibit characteristic differences in their cardinal points of growth. In Kysoor f growth is arrested at. the. temperature minimum, of 22°C. The optimum temperature is at 34°C., after which growth-rate declines and becomes'completely arrested at 58°C. At 60°C. there is a sudden spasmodic contraction of death.

.. In other;/plants the cardinal points are different. In some plants the ;; optimum growth is attained, at 28°C. and remains constant up .to 38°0. Chemical agents are found to exert characteristic actions on growth. The method of investigation sketched here opens out an extended field of investigation. The effect of a 'chemical substance, I find, to be modified by (1) the strength of the solution, (2.) the duration of application, and (3) the condition of the tissue. A poisonous substance in minute doses is often found to exert a stimulating action. Too long continued action of a stimulant, on the ' other hand, exerts a depressing effect. The influence of the tonic condition is shown .by the fact that while a given dilution of a poisonous substance ’ kills a weak specimen, the same poisonous solution, applied to a vigorous specimen, actually . stimulates and enhances the rate of the growth. I give' below descriptions of a few typical re¬ actions.

The reagent, when in a liquid form, is locally applied v oi the growing : organ. The records, taken .before and' after the application, exhibit the stimulatory ' or . depressing character of the reagent. A different method of applica¬ tion of the reagent is, employed for plants with extended region of growth. The specimen is then enclosed in a glass cylinder, with inlet and outlet pipes. The cylinder Is first filled with water, and the normal rate of growth recorded. This rate remains constant for several hours; but prevention of access of air for too long a time affects the normal growth. After obtaining normal record, water charged with the giving chemical agent is passed' into the cylinder ; and the subsequent record shows the character¬ istic effect of the reagent. The introduction of a gas into the chamber offers no difficulty.

Hydrogen Peroxide: Experiment 62 .—This reagent, as supplied by Messrs. Parke Davis & Co., was diluted to 1 per cent, and applied to the growing plant. Its stimulating action on growth is demonstrated' in the right hand record of Fig. 68a, where the rate of growth is seen enhanced two and a half times the normal rate. Fig. 68.—Effect of chemical agents : (a) Acceleration of growth under H„0 2) (5) Effect of NH a , preliminary acceleration followed by retardation, (c) Effect of ether (E) and recovery (A).

seen in the middle record of Fig. 686, where the rat£ is seen to be double the normal. Continued action, however, caused a depression ; the third record of this series shows' this, where the reduction is three-fourths of the normal rate. Ether * Experiment 64 .—In Fig. 68c, the records exhibit the effect of introduction of ether vapour into the plant chamber, and its recovery after the removal of the vapour. Ether is seen -to depress the rate of growth to a little more than a third of the normal rate. The recovery is seen to be nearly complete half an hour after the removal of the vapour.

Carbonic Acid; Experiment 65 .—The action of this gas is very remarkable. The plant was immersed in water with water, charged with carbonic acid gas. This induced a very marked acceleration of growth (Fig. 69). In a seed¬ ling ' of Onion, the increase half times. In the flower bud ifep of Crinum , the rate was found enhanced threefold from the normal 0*25 p to 0-75 p per second. After this preliminary enhancement, there was a de- pression of growth within lA minutes of the application, the

rate being now rednced to 015 p per second. These effects were found to take place equally in light or in darkness." Goal Gas: Experiment 66.— Coal gas induces a depres¬ sion. It is curious that subjection to the action of this gas does not produce so evil an effect as one would expect. The introduction of the gas had reduced the growth-rate to more than half; but there was a recovery half an hour after the introduction of fresh air. Sulphuretted Hydrogen : Experiment 67. —This gas not only exerts a depressing effect, but its after-effect is also very ’persistent. The plant experimented on was very vigorous and its rate of growth was depressed to half by subjection to the action of the gas for a short time, a he record taken half an hour after the introduction of fresh air did not exhibit any recovery.

dilute solution retards growth, and in stronger solution acts as a poison. The following results were obtained with a wheat seedling under different strengths of solution; Copper Sulphate: Experiment 69 .—The effect of a solu¬ tion of this reagent is far more depressing than the last. One per cent, solution acting for a short time depressed the rate from 0-45 ? to 0-13 ? per sec. Long continned action ef the poisonous solution kills the plant. The effect of a chemical agent is modified by the strength of the solution, the duration of application and the tonic condition of the tissue.