The Power of Movement in Plants Part 19

(16.) Eucalyptus resinifera (Myrtaceae, 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 a.s.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 day it was observed more frequently; and two tracings were made (see A and B, Fig. 108), as a single one would have been too complicated. The apex changed its course 13 times in the course of 16 h., chiefly up and down, but with some lateral movement. The actual amount of movement in any one direction was small.

Fig. 108. Eucalyptus resinifera: circ.u.mnutation of a leaf, traced, A, from 6.40 A.M. to 1 P.M. June 8th; B, from 1 P.M. 8th to 8.30 A.M. 9th. Apex of leaf 14 inches from the horizontal gla.s.s, so figures considerably magnified.

(17.) Dahlia (garden var.) (Compositae, Fam. 122).--A fine young [page 245]

leaf 5 3/4 inches in length, produced by a young plant 2 feet high, growing vigorously in a large pot, was directed at an angle of about 45o beneath the horizon. On June 18th the leaf descended from 10 A.M. till 11.35 A.M.

(see Fig. 109); it then ascended greatly till 6 P.M., this ascent being probably due to the light

Fig. 109. Dahlia: circ.u.mnutation of leaf, traced from 10 A.M. June 18th to 8.10 A.M. 20th, but with a break of 1 h. 40 m. on the morning of the 19th, as, owing to the gla.s.s filament pointing too much to one side, the pot had to be 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 gla.s.s in the line of its inclination, and 4 3/4 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 gla.s.s.

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day the leaf descended from 8.20 A.M. till 7.15 P.M., 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 distances 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.) Mutisia clematis (Compositae).--The leaves terminate in tendrils and circ.u.mnutate 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 2o, the second 21o, and the third 10o higher than in the middle of the day; so that instead of sinking they rise a little at night.

(19.) Cyclamen Persic.u.m (Primulaceae, Fam. 135).--A young leaf, 1.8 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 afterwards, 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 gla.s.s filament rested between 5 and 6 P.M. on the rim of the pot. The amount of movement was considerable; for if we a.s.sume that the whole leaf 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.

* 'The Movements and Habits of Climbing Plants,' 1875, p. 118.

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(20.) Allamanda Schottii (Apocyneae, Fam. 144).--The young leaves of this shrub are elongated, with the blade bowed so much

Fig. 110. Cyclamen Persic.u.m: circ.u.mnutation of leaf, traced from 6.45 A.M.

June 2nd to 6.40 A.M. 5th. Apex of leaf 7 inches from the vertical gla.s.s.

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, 4 3/4 inches in length, stood at 2.50 P.M. on [page 248]

Dec. 5th at an angle of 13o beneath the horizon, but by 9.30 P.M. the blade had straightened itself so much, which implies the raising of the apex, that the chord now stood at 37o above the horizon, and had therefore risen 50o. On the next day similar angular measurements of the same leaf were made; and at noon the chord stood 36o beneath the horizon, and 9.30 P.M. 3 1/2o above it, so had risen 39 1/2o. The chief cause of the rising movement lies in the straightening of the blade, but the short petiole rises between 4o and 5o. On the third night the chord stood at 35o above the horizon, and if the leaf occupied the same position at noon, as on the previous day, it had risen 71o. 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 exposure to a strong light is apparently requisite for the periodical change of curvature in the blade, and for the slight rising of the petiole.

(21.) Wigandia (Hydroleaceae, 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 cla.s.sed amongst sleeping plants.

Fig. 111. Petunia violacea: downward movement and circ.u.mnutation of a very young leaf, traced from 10 A.M. June 2nd to 9.20 A.M. June 6th. N.B.--At 6.40 A.M. on the 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 the diagram. Apex of leaf 7 inches from the vertical gla.s.s. Temp. generally 17 1/2o C.

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(22.) Petunia violacea (Solaneae, Fam. 157).--A very young leaf, only 3/4 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 horizontal. The strongly marked zigzag line in the figure on p. 248 (Fig. 111), shows that this was effected by modified circ.u.mnutation; and during the latter part of the time there was much ordinary circ.u.mnutation 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 more horizontal as it grew older. The angles which two older leaves formed together, were measured in the evening and about noon on 3 successive days, and each night the angle decreased a little, though irregularly.

Fig. 112. Acanthus mollis: circ.u.mnutation of young leaf, traced from 9.20 A.M. June 14th to 8.30 A.M. 16th. Apex of leaf 11 inches from the vertical gla.s.s, so movement considerably magnified. Figure here reduced to one-half of original scale. Temp. 15o - 16 1/2o C.

(23.) Acanthus mollis (Acanthaceae, Fam. 168).--The younger of two leaves, 2 1/4 inches in length, petiole included, produced by a seedling plant, was observed during 47 h. Early on each of the three mornings, the apex of the leaf fell; and it continued to fall till 3 P.M., on the two afternoons when observed. 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 epinastic growth more and more horizontal; 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 rose every night; and the rise between noon and 10.15 P.M., when measured on one occasion, was 10o. This rise was chiefly [page 250]

or exclusively due to the straightening of the blade, and not to the movement of the petiole. We may therefore conclude that the leaves of Acanthus circ.u.mnutate periodically, falling in the morning and rising in the afternoon and night.

(24.) Cannabis sativa (Cannabineae, 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 8 A.M. May 29th and at 10.30 P.M. were considerably declined. On a subsequent day two leaves stood at 2 P.M. at 21o and 12o beneath the horizon, and at 10 P.M. at 38o beneath it. Two other leaves on a younger plant were horizontal at 2 P.M., and at 10 P.M. had sunk to 36o 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 (Coniferae, 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 circ.u.mnutating. The same 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 leaf, 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. 1st. On August 1st it circ.u.mnutated about the same small s.p.a.ce, 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 plant by Dr. Carl Kraus' paper, 'Beitrage zur Kentniss der Bewegungen Wachsender Laubblatter,' Flora, 1879, p. 66. We regret that we cannot fully understand parts of this paper.

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the leaf manifestly circ.u.mnutated. 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

Fig. 113. Pinus pinaster: circ.u.mnutation 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 14 inches from the vertical gla.s.s, 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 [page 252]

quite fully grown, produced by a lateral shoot, on a young tree 3 feet in height, were observed during 29 h. (July 31st), in the same manner as the leaves of the previous species. Both these leaves certainly circ.u.mnutated, making within the above period two, or two and a half, small, irregular ellipses.

(26.) Cycas pectinata (Cycadeae, Fam. 224).--A young leaf, 11 inches in length, of which the leaflets had only recently become uncurled, was observed during 47 h. 30 m. The main petiole was secured to a stick at the base of the two terminal leaflets. To one of the latter, 3 3/4 inches in length, a filament was fixed; the leaflet was much bowed downward, but as the terminal 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 6.40 A.M. 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.

Fig. 114. Cycas pectinata: circ.u.mnutation of one of the terminal leaflets, traced from 8.30 A.M. June 22nd to 8 A.M. June 24th. Apex of leaflet 7 3/4 inches from the vertical gla.s.s, so tracing not greatly magnified, and here reduced to one-third of original scale; temp. 19o - 21o C.

CIRc.u.mNUTATION OF LEAVES: MONOCOTYLEDONS.

(27.) Canna Warscewiczii (Cannaceae, Fam. 2).--The movements of a young leaf, 8 inches in length and 3 in breadth, produced by a vigorous young plant, were observed during 45 h. 50 m., as 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 the two figures are continuous in time. The movement is periodical, as the leaf descended from the early morning until about 5 P.M., and ascended during the rest of the evening and [page 253]

part of the night. On the evening of the 11th it circ.u.mnutated on a small scale for some time about the same spot.

Fig. 115. Canna Warscewiczii: circ.u.mnutation of leaf, traced (A) from 11.30 A.M. June 10th to 6.40 A.M. 11th; and (B) from 6.40 A.M. 11th to 8.40 A.M.

12th. Apex of leaf 9 inches from the vertical gla.s.s.

(28.) Iris pseudo-acorus (Irideae, Fam. 10).--The movements of a young leaf, rising 13 inches above the water in which the plant grew, were traced as shown in the figure (Fig. 116), during 27 h. 30 m. It manifestly circ.u.mnutated, 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 8 h. 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.

Fig. 116. Iris pseudo-acorus: circ.u.mnutation of leaf, traced from 10.30 A.M. May 28th to 2 P.M. 29th. Tracing continued to 11 P.M., but not here copied. Apex of leaf 12 inches beneath the horizontal gla.s.s, so figure considerably magnified. Temp. 15o - 16o C.

(29.) Crinum Capense (Amaryllideae, Fam. 11).--The leaves of this plant are remarkable for their great length and narrowness: one was measured and found to be 53 inches long and only 1.4 broad at the base. Whilst quite young they stand up almost vertically to the height of about a foot; afterwards [page 254]

their tips begin to bend over, and subsequently hang vertically down, and thus continue to grow. A rather young leaf was selected, of which the dependent tapering point was as yet only 5 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-gla.s.s 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 been

Fig. 117. Crinum Capense: circ.u.mnutation of dependent tip of young leaf, traced on a bell-gla.s.s, 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.M. on this day is alone here given. As we see in the figure, there can be no doubt that the apex of this leaf circ.u.mnutated.

A gla.s.s 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 movements were traced from 3 P.M. May 22nd to 10.15 A.M. 25th. The leaf was growing rapidly, so that the apex ascended greatly during this period; as it zigzagged much it was clearly circ.u.mnutating, and it apparently tended to form one ellipse each 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 rise 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, [page 255]

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 circ.u.mnutation, was 3 1/8 inches in the course of 20 h. During the next 24 h. it travelled 2 inches. The circ.u.mnutating movement, therefore, of this young leaf was strongly marked.

(30.) Pancratium littorale (Amaryllideae).--The movements, much magnified, of a leaf, 9 inches in length and inclined at about 45o 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 circ.u.mnutation of the leaf.

(31.) Imatophyllum vel Clivia (sp.?) (Amaryllideae).--A long gla.s.s filament was fixed to a leaf, and the angle formed by it with the horizon was measured occasionally during three successive 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 48o, and the largest 50o; so that it rose only 2o 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.

(32.) Pistia stratiotes (Aroideae, Fam. 30).--Hofmeister remarks that the leaves of this floating water-plant are more highly inclined at night than by day.* We therefore fastened a fine gla.s.s filament to the midrib of a moderately young leaf, and on Sept. 19th measured the angle which it formed with the horizon 14 times between 9 A.M. and 11.50 P.M. The temperature of the hot-house varied during the two days of observation between 18 1/2o and 23 1/2o C. At 9 A.M. the filament stood at 32o above the horizon; at 3.34 P.M. at 10o and at 11.50 P.M. at 55o; these two latter angles being the highest and the lowest observed during the day, showing a difference of 45o. The rising did not become strongly marked until between

* 'Die Lehre von der Pflanzenzelle,' 1867, p. 327.

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5 and 6 P.M. On the next day the leaf stood at only 10o above the horizon at 8.25 A.M., and it remained at about 15o till past 3 P.M.; at 5.40 P.M.

it was 23o, and at 9.30 P.M. 58o; so that the rise was more sudden this evening than on the previous one, and the difference in the angle amounted to 48o. The movement is obviously periodical, and as the leaf stood on the first night at 55o, and on the second night at 58o above the horizon, it appeared very steeply inclined. This case, as we shall see in a future chapter, ought perhaps to have been included under the head of sleeping plants.

(33.) Pontederia (sp.?) (from the highlands of St. Catharina,