The Power of Movement in Plants

Dionea muscipula : closure of the lobes and circumnutation of a full-grown leaf, whilst absorbing an infusion of raw meat, traced in darkness, from 7.15 P.M. Sept. 24th to 9 a.m. 26th. Apex of leaf 84 inches from the vertical glass. Figure here reduced to two-thirds of original scale. strongly zigzag, and this indicates that the closing of the lobes was combined with the circumnutation of the whole leaf, and there cannot be much doubt, considering how motionless the leaf was during 2 h. 30 m. before it received the infusion, that the absorption of the animal matter had excited it to circumnutate. The leaf was occasionally observed for the next four days, but was kept in rather too cool a place; nevertheless, it continued to circumnutate to a small extent, and the lobes remained closed.

It is sometimes stated in botanical works that the lobes close or sleep at night; but this is an error. To test the statement, very long glass filaments were fixed inside the two lobes of three leaves, and the distances between their tips were measured in the middle of the day and at night; but no difference could be detected. The previous observations relate to the movements of the whole leaf, but the lobes move independently of the petiole, and

seem to be continually opening and shutting to a very small extent. A nearly full-grown leaf (afterwards proved to be highly sensitive to contact) stood almost horizontally, so that by driving a long thin pin through the foliaceous petiole close to the blade, it was rendered motionless. The plant, with a little triangle of paper attached to one of the marginal spikes, was placed under a microscope with an eye-piece micrometer, each division of which equalled =3, of an iuch. The apex of the paper-triangle was now seen to be in constant slight move- ment; for in 4h. it crossed nine divisions, or =%, of an inch, and after ten additional hours it moved back and had crossed sq in an opposite direction. The plant was kept in rather too cool a place, and on the following day it moved rather less, namely, <3, in 3 h., and 2, in an opposite direction during the next 6 h. The two lobes, therefore, seem to be constantly closing or opening, though to a very small distance; for we must remember that the little triangle of paper affixed to the marginal spike increased its length, and thus exaggerated somewhat the movement. Similar observations, with the important difference that the petiole was left free and the plant kept under a high temperature, were made on a leaf, which was healthy, but so old that it did not close when its sensitive hairs were repeatedly touched, though judging from other cases it would have slowly closed if it had been stimulated by animal matter. The apex of the triangle was in almost, though not quite, constant movement, sometimes in one direction and sometimes in an opposite one; and it thrice crossed five divisions of the micrometer (i.e. ~}; of an inch) in 80 m.

This movement on so small a scale is hardly comparable with ordinary circumnutation; but it may perhaps be compared with the zigzag lines and little loops, by which the larger ellipses made by other plants are often interrupted. In the first chapter of this volume, the remarkable oscillatory movements of the circumnutating hypocotyl of the cabbage lave been described. The leaves of Dionwa present the same phenomenon, which is a wonderful one, as viewed under a low power (2-inch object-glass), with an eye-piece micrometer o! which each division (;4, of an inch) appeared as a rather wide space. The young unexpanded leaf, of which the circumnutating movements were traced (Fig. 106), had a glass filament fixed perpendicularly to it; and the movement of the apex was observed in the hot-house (temp. 84° to 86° F.), with light admitted only from above, and with any lateral currents of air

excluded. The apex sometimes crossed one or two divisions of the micrometer at an imperceptibly slow rate, but generally it moved onwards by rapid starts or jerks of +35 or rsz, and in one instance of ;455 of an inch. After each jerk forwards, the apex drew itself backwards with comparative slowness for part of the distance which had just been gained; and then after a very short time made another jerk forwards. Four conspi- cuous jerks forwards, with slower retreats, were seen on one occasion to occur in exactly one minute, besides some minor oscillations. As far as we could judge, the advancing and retreating lines did not coincide, and if so, extremely minute ellipses were each time described. Soinetimes the apex remained quite motionless for a short period. Its general course during the several hours of observation was in two opposite directions, so that the leaf was probably circumnutating.

An older leaf with the lobes fully expanded, and which was afterwards proved to be highly sensitive to contact, was next observed in a similar manner, except that the plant was exposed to a lower temperature ina room. The apex oscillated forwards and backwards in the same manner as before; but the jerks for- ward were less in extent, viz. about 745 inch; and there were longer motionless periods. As it appeared possible that the movements might be due to currents of air, a wax taper was held close to the leaf during one of the motionless periods, but no oscillations were thus caused. After 10 m., however, vigorous oscillations commenced, perhaps owing to the plant having been warmed and thus stimulated. Thecandle was then removed and before long the oscillations ceased ; nevertheless, when looked at again after an interval of 1h. 30m., it was again oscillating. The plant was taken back into the hot-house, and on the following morning was seen to be oscillating, though not very vigorously. Another old but healthy leaf, which was not in the least sensitive to a touch, was likewise observed during two days in the hot-house, and the attached filament made many little jerks forwards of about +345 or only zgq of an inch.

Finally, to ascertain whether the lobes independently of the petiole oscillated, the petiole of an old leaf was cemented close to the blade with shellac to the top of a little stick driven into the soil. But before this was done the leaf was observed and found to be vigorously oscillating or jerking; and after it had been cemented to the stick, the oscillations of about +255 of an inch stil] continued. On the following day a little infusion of raw meat was placed on the leaf, which caused the lobes tc close together very slowly in the course of two days; and the oscillations continued during this whole time and for the next two days. After nine additional days the leaf began to open and the margins were a little everted, and now the apex of the glass filament remained for long periods motionless, and then moved backwards and forwards for a distance of about z455 of an inch slowly, without any jerks. Nevertheless, after warming the leaf with a taper held close to it, the jerking movement recommenced.

This same leaf had been observed 2} months previously, and was then found to be oscillating or jerking. We may therefore infer that this kind of movement goes on night and day fora very long period; and it is common to young unexpanded leaves and to leaves so old as to have lost their sensitiveness to a touch, but which were still capable of absorbing nitrogenous matter. The phenomenon when well displayed, as in the young leaf just described, is a very interesting one. It often brought before our minds the idea of effort, cr of a small animal struggling to escape from some constraint.

(16.) Lucalyptus resinifera (Myrtacee, Fam. 94).—A young leaf, two inches in length together with the petiole, produced by a lateral shoot from a cut-down tree, was observed in the usual manner, The blade had not as yet as- sumed its vertical position. On June 7th only a few observations were made, and the tracing merely showed that the leaf had moved three times upwards and three downwards. On the following Eucalyptus resinifera : circumnu- day it was observed more fre-

tation of a leaf, traced, A, from quently; and two tracings were from the horizontal glass, so complicated. The apex changed figures considerably magnified, its course 13 times in the course ; of 16h., chiefly up and down, but with some lateral movement. The actual amount of movement in any one direction was small. Icaf 53 inches in length, produced by a young plant 2 feet high, growing vigorously in a large pot, was directed at an angie ot about 45° beneath the horizon. On June 18th the leaf descended from 10 a.m. till 1135 a.m. (see Fig. 109); it then ascended greatly till 6 p.wt., this ascent being probably due to the light

Dahha: circumnutation of leaf, traced from 10 a.m. June 18th to 8.10 a.m, 20th, but with a break of Lh. 40m. on the morning of the 19th, as, owing to the glass filament pointing too much to one side, the pot had to ke slightly moved ; therefore the relative position of the two tracings is somewhat arbitrary. The figure here given is reduced to one-fifth of the original scale. Apex of leaf 9 inches from the glass in the line of its inclination, and 4% in a horizontal line,

coming only from above. It zigzagged between 6 P.m. and 10.35 p.m., and ascended a little during the night. It should be remarked that the vertical distances in the lower part of the diagram are much exaggerated, as the leaf was at first deflected beneath the horizon, and after it had sunk downwards, the filament pointed in a very oblique line towards the glass. Next day the leaf descended from 8.20 a.m. till 7.15 p.x., then zigzagged and ascended greatly during the night. On the morning of the 20th the leaf was probably beginning to descend, though the short line in the diagram is horizontal. The actual distancce travelled by the apex of the leaf were considerable, but could not be calculated with safety. From the course pursued on the second day, when the plant had accommodated itself to the light from above, there cannot be much doubt that the leaves undergo a daily periodic movement, sinking during the day and rising at night.

(18.) Mulisia cl-matis (Composite).—The leaves terminate in tendrils and circumnutate like those of other tendril-bearers; but this plant is here mentioned, on account of an erroneous statement * which has been published, namely, that the leaves sink at night and rise during the day. The leaves which behaved in this manner had been kept for some days in a northern room and had not been sufficiently illuminated. A plant therefore was left undisturbed in the hot-house, and three leaves had their angles measured at noon and at 10 p.m. All three were inclined a little beneath the horizon at noon, but one stood at night 2°, the second 21°, and the third 10° higher than in the middle of the day; so that instead of sinking they rise a little at night.

(19.) Cyclumen Persicim (Primulacee, Fam. 135).—A young leaf, 18 of an inch in length, petiole included, produced by an old root-stock, was observed during three days in the usual manner (Fig.110). On the first day the leaf fell more than after- wards, apparently from adjusting itself to the light from above. On all three days it fell from the early morning to about 7 p.m., and from that hour rose during the night, the course being slightly zigzag. The movement therefore is strictly periodic. It should be noted that the leaf would have sunk each evening a little lower down than it did, had not the glass filament rested between 5 and 6 p.m. on the rim of the pot. The amount of movement was considerable; for if we assume that the whole Icaf to the base of the petiole became bent, the tracing would be magnified rather less than five times, and this would give to the apex a rise and fall of half an inch, with some lateral movement. This amount, however, would not attract attention without the aid of a tracing or measurement of some kind.

20.) Allamandu Schottii (A pocynex, Fam. 144).—The young leaves of this shrub are elongated, with the blado bowed so much OS pm 4h Cyclamen Persicum ; circumnutation of leaf, traced from 6.45 a.m June 2ad to 6.40 A.M. Sth, Apes of leaf 7 inches from the vertical glass, downwards as almost to form a semicircle. The chord—that is, a line drawn from the apex of the blade to the base of the petiole—of a young leaf. 43 inches in length, stood at 2.50 p.m on

Petunia violice:: downward meove- ment and circumnutation of a very young leaf, traced from 1) A.M. June 2nd to 9.20 a.m. June 6th. N.B.—At 6.40 a.m. on tne 5th it was necessary to move the pot a little, and a new tracing was begun at the point where two dots are not joined in tne diagram. Apex of lea? 7 inches from the vertical glass. Temp. generally 174°C. the blade had straightened itself so much, which implies the raising of the apex, that the chord now stood at 37° above the horizon, and had therefore risen 5U°. On the next day similar angular measurements of the same leaf were made; and at noon the chord stood 36° be- neath the horizon, and 9.30 p.s. 34° above it, so had risen 393°. The chief cause of the rising movement lies in the straighten- ing of the bldde, but the short petiole rises between 4° and 5°. On the third night the chord stood at 35° above the horizon, and if the leaf occupied the same position at noon, as on the previous day, it had risen 71°. With older leaves no such change of curvature could be detected. The plant was then brought into the house, and kept in a north-east room, but at night there was no change in the curvature of the young leaves; so that previous expo- sure to a strong light is appa- rently requisite for the periodi- cal change of curvature in the blade, and for the slight rising of the petiole.

(21.) Wiyandia (Hydroleacer, Fam. 149).—Professor Pfeffer informs us that the leaves of this plant rise in the evening; but as we do not know whether or not the rising is great, this species ought perhaps to be classed amongst sleeping plants (22.) Petunia violacea (Solanew, Fam. 157).—A very young leaf, only 2 inch in length, highly inclined upwards, was observed for four days. During the whole of this time it bent outwards and downwards, so as to become more and more nearly hori- zontal. The strongly marked zigzag line in the figure on p. 248 (Fig. 111), shows that this was effected by modified circum- nutation ; and during the latter part of the time there was much ordinary circumuutation on a small scale. The movement in the diagram is magnified between 10 and 11 times. It exhibits a clear trace of periodicity, as the leaf rose a little each evening ; but this upward tendency appeared to be almost conquered by the leaf striving to become more and Fig. 112, more horizontal as it grew older. The angles which two older leaves formed together, were measured in the even- ing and about noon on 3 successive days, and each night the angle de- creased a little, though irregularly.

Fam. 168).—The younger of two leaves, 2} inches in length, petiole included, produced by a seedling plant, was observed during 47 h. Early on each of the three morn- ings, the apex of the leaf fell; and it continued to fall till 3 p.m, on the two afternoons when observed. A After 3 p.m. it rose considerably, and / continued to rise on the second night until the early morning. But on the first night it fell instead of rising, and we have little doubt that this

was owing to the leaf being very young and becoming through epi- nastic growth more and more hori- zontal; for it may be seen in the diagram (Fig. 112), that the leaf stood on a higher level on the first than on the second day. The leaves of an allied species (A. spinosus) certainly from 9.20 a.m. June 14th to 8.30 A.M. 16th. Apex of leaf 11 inches from the vertical glass, so movement considerably magnified. Figure here reduced to one- half of original scale. Temp. 15°-163° C.

rose every night ; and the rise between noon and 10.15 p.m., or exclusively due to the straightening of the blade, and not to the movement of the petiole. We may therefore concl ude that the leaves of Acanthus circumnutate periodically, falling in the morning and rising in the afternoon and night. (24.) Cannabis sutiva (Cannabinew, Fam. 195).—We have here the rare case of leaves moving downwards in the evening, but not to a sufficient degree to be called sleep.* In the early morning, or in the latter part of the night, they move upwards. For instance, all the young leaves near the summits of several stems stood almost horizontally at 8a.m. May 29th, and at 10.30 p.m. were considerably declined. On a subsequent day two leaves stood at 2 p.m. at 21° and 12? beneath the horizon, and at 10 p.m. at 38° beneath it. wo other leaves on a younger plant were horizontal at 2 p.m.,and at 10 p.m. had sunk to 36° beneath the horizon. With respect to this downward movement of the leaves, Kraus believes that it is due to their epinastic growth. He adds, that the leaves are relaxed during the day, and tense at night, both in sunny and rainy weather.

(25.) Pinus pinaster (Coniferee, Fam. 223).—The leaves on the summits of the terminal shoots stand at first in a bundle almost upright, but they soon diverge and ultimately become almost horizontal. The movements of a young leaf, nearly one inch in length, on the summit of a seedling plant only 3 inches high, were traced from the early morning of June 2nd to the evening of the 7th. During these five days the leaf diverged, and its apex descended at first in an almost straight line; but during the two latter days it zigzagged so much that it was evidently cireumnu- tating. Thesame little plant, when grown to a height of 5 inches, was again observed during four days. A filament was fixed transversely to the apex of a Jeaf, one inch in length, and which had already diverged considerably from its originally upright position. It continued to diverge (see A, Fig. 113), and to descend from 11.45 a.m. July 31st to 6.40 a.m. Aug. Ist. On August Ist it circumnutated about the same small space, and again descended at night. Next morning the pot was moved nearly one inch to the right, and a new tracing was begun (B), From this time, viz., 7 a.m. August 2nd to 8.20 a.m. on the 4th

* We were led to observe this Flcra, 1879, p.66. We regrc-t that plant by Dr. Carl Kraus’ paper, we cannot fully underet ‘ Beitrige zur Kentriss der Bewe- of this paper. Bn Tae gungen Wacksender Laubblatter,’ the leaf manifestly cireumnutated. It does not appear from the diagram that the leaves move periodically, for the descending course during the first two nights, was clearly due to epinastic Pinus pinaster: circumnutation of young leaf, traced from 11.45 a.m. July 31st to 8.20 a.m..Aug. 4th. At 7 A.M. Aug. 2nd the pot was moved an inch to one side, so that the tracing consists of two figures. Apex of leaf 144 inches from the vertical glass, so movements much magnified.

growth, and at the close of our observations the leaf was not nearly so horizontal as it would ultimately become. Pinus austriaca.—Two leaves, 3 inches in length, but not 252 Cuap. 1V. quite fully grown, produced by a lateral shoot, on a young tree 3 feet in height, were observed during 29h. (July 81st), in the same manner as the leaves of the previous species. Both these Qycas pectinata : circum- nutation of one of the terminal leaflets, traced from 8.30 a.M. June 22nd to 8 aM. June 24th, Apex of leatlet 7% inches from the ver- tical glass, so tracing not greatly magnified, and here reduced to one-third of original scale; temp. 19°-21°C,

leaves certainly circumnuta‘ed, making within the above period two, or two and a half, small, irregular ellipses. (26.) Cycas pectinate (Cycader, Fam 294),— A young leaf, 114 inches in length, of which the leaflets had only recently become uncurled, was observed during 47h. 30m. The main petiole was secured to a stick at the base of the two terminal leaflets. To one of the latter, 3% inches in length, a filament was fixed; the leaflet was much bowed downward, but as the terminai part was upturned, the filament projected almost horizontally. The leaflet moved (see Fig. 114) largely and periodically, for it fell until about 7 p.m. and rose during the night, falling again next morning after 640 am. The descending lines are in a marked manner zigzag, and so probably would have been the ascending lines, if they had been traced throughout the night.

(27.) Canna Warscewiczti (Cannacce, Fam. 2).—The movements of a young leaf, 8 inches in length and 83 in breadth, produced by a vigorous young plant, were observed during 45 h, 501m., a8 shown in Fig. 115. The pot was slided about an inch to the right on the morning of the 11th, as a single figure would have been too complicated; but periodical, as the leaf descended from the early morning until about 5pm., and ascended during the rest of the evening and

(28.) Iris pseudo-acorus (Iridee, Fam. 10).—The movements of a young leaf, rising 18 inches above the water in which the plant grew, were traced as shown in the figure (Fig. 116), during 27 h. 30m. It manifestly circumnutated, though only to a small extent. On the second morning, between 6.40 a.m. and 2 P.M. (at which latter hour the figure here given ends), the apex changed its course five times. During the next 8h. 40 m. it zigzagged much, and descended as far as the lowest dot in the figure, making in its course two very small ellipses; but if these lines had been added to the diagram it would have been too complex.

(29.) Crinum Cupense (Amaryllidez, Fam. 11).—The leaves of this plant are remarkable for their great length and narrowness: one was measured and found to be 58 inches long and only 1:4 broad at the base. nutation of leaf, traced from 10.30 a.m. May 28th to2 pM. 29th, Tracing continued to 11 P.m., but not here copied. Apex of leaf 12 inches beneath the horizontal glass, so figure considerably mag- nified. Temp. 15°-16°C. their tips begin to bend over, and subscquenily hang vertically down, and thus continue to grow. A rather young leaf was selected, of which the dependent tapering point was as yet only 54 inches in length, the upright basal part being 20 inches high, though this part would ultimately become shorter by being more bent over. A large bell-glass was placed over the plant, with a black dot on one side; and by bringing the dependent apex of the leaf into a line with this dot, the accompanying figure (Fig. 117) was traced on the other side of the bell, during 2: days. During the first day (22nd) the tip travelled laterally far to the left, perhaps in consequence of the plant having Leen

Crinum capense ; circumnutation of dependent tip of young leaf, traced on a bell-glass, from 10.30 P.M. May 22nd to 10.15 a.m. 25th. Figure not greatly magnified. disturbed; and the last dot made at 10.30 p.s1. on this day is alone here given. As we see in the figure, there can be no doubt that the apex of this leaf cireumnutated. A glass filament with little triangles of paper was at the same time fixed obliquely across the tip of a still younger leaf, which stood vertically up and was as yet straight. Its move- ments were traced from 3pm. May 22nd to 1915 am. 25th. The leaf was growing rapidly, so that the apex ascended greatly during this period ; as it zigzagged much it was clearly circum- nutating, and it apparently tended to form one ellipse cach day. The lines traced during the night were much more vertical than those traced during the day; and this indicates that the tracing would have exhibited a nocturnal rice and a diurnal fall, if the leaf had not grown so quickly. The movement of this same leaf after an interval of six days (May 31st), by which time the tip had curved outwards into a horizontal position,

and had thus made the first step towards becoming dependent, was traced orthogonically by the aid of a cube of wood (in the manner before explained); and it was thus ascertained that the actual distance travelled by the apex, and due to circumnutation, was 33 inches in the course of 204 h. During the next 24h. it travelled 25 inches. The circumnutating movement, therefore, of this young leaf was strongly marked. (80.) Paneratium littorale (Amaryllidew).—The movements, much magnified, of a leaf, 9 inches in length and inclined at about 45° above the horizon, were traced during two days. On the first day it changed its course completely, upwards and downwards and laterally, 9 times in 12 h.; and the figure traced apparently represented five ellipses. On the second day it was observed seldomer, and was therefore not seen to change its course so often, viz., only 6 times, but in the same complex manner as before. The movements were small in extent, but there could be no doubt about the circumnutation of the leaf.

(81.) Imatophyllum. vel Clivia (sp.?) (Amaryllides).—A long glass filament was fixed to a leaf, and the angle formed by it with the horizon was measured occasionally during three suc- cessive days. It fell each morning until between 3 and 4 P.m., and rose at night. The smallest angle at any time above the horizon was 48°, and the largest 50°; so that it rose only 2° at night; but as this was observed each day, and as similar observations were nightly made on another leaf on a distinct plant, there can be no doubt that the leaves move periodically, though to a very small extent. The position of the apex when it stood highest was ‘8 of an inch above its lowest point.