The Power of Movement in Plants

The hypocotyl is rather thick, about +12 of inch; nevertheless it circumnutated in a complex course, though to a small extent. The movement of an old seedling with two true leaves partially developed, was observed in the daik. As the movement was magnified about 100 times it is not trustworthy and is not given; but there could be no doubt that the hypocotyl moved in all directions during the day, changing its course 19 times. The extreme actual distance from side to side through which the upper part of the hypocotyl passed in the course of 144 hours was only 4 of an inch; it sometimes travelled at the rate of gs Of an inch in an hour.

Cucurbita ov'fera: course followed hy a radicle in bending geotropically downwards, traced on a horizontal glass, between 11.25 A.M and 10.25 P.M.; the direction during the night is indicated by the broken line. Movement of bead magnified 14 times. germinated on damp sand was fixed so that the slightly curved radicle, which was only ‘07 inch in length, stood almost vertically upwards, in which position geotropism would act at first with little power. A filament was attached near to its base, and projected at about an-angle of 45° wbove the horizon. The general course followed during the 11 hours of observation and during the following night, is shown in the accompanying diagram (Fig. 26), and was plainly due to geotropism; but it was also clear that the radiclo circumnutated. By the next morning the tip had curved so much downwards that the fila- ment, instead of projecting at 45° above the horizon, was nearly horizontal. Another germinating seed was turned upside down and covered with damp sand; and a filament was fastened to the radicle so as to project at an angle of about 50° above the horizon ; this radicle was °35 of an inch in length and a little curved. The course pursued was mainly governed, as in the last case, by geotropism, but the line traced during 12 hours and magnified as before was more strongly zigzag, again showing circumnutation.

Four radicles were allowed to grow downwards over plates of smoked glass, inclined at 70° to the horizon, under the Fig. 27. Cucurbita ovifera: circumnuta- A. B. tion of arched hypocotyl at Cucurbita ovifera: tracks a very early age, traced in left by tips of radicles darkness on a horizontal glass, in growing downwards from 8 4.M. to 10.20 A.M. on over smoked — glass- the following day. The move- plates, inclined at 70° ment of the bead magnified to the horizon, 20 times, here reduced to one-

tracks; and a third short one was almost as plainly serpentine as that at A. It was also manifest by a greater or less amount of soot having been swept off the glasses, that the tips had pressed alternately with greater and lcss force on them. There must, therefore, have }-en movement in at Icast two planes at right angles to one a.other. These radicles were so delicate that they rarely had the power to sweep the glasses quite clean. One of them had developed some lateral or secondary rootlets, which projected w few degrees beneath the horizon; and it is an im- portant fact that three of them left distinctly serpentine tracks on the smoked surface, showing beyond doubt that they had circumnutated like the main or primary radicle. But the tracks were so slight that they could not be traced and copied after the smoked surface had been varnished.

Hypocotyl.—A seed lying on damp sand was firmly fixed by two crossed wires and by its own growing radicle. The cotyle- dons were still enclosed within the seed-coats; and the short fastened transversely across movement from left to right in the its upper end, traced in dark- fiouye were parallel to the plane ness on a horizontal glass, : about 18 times, here only 43 thom out of the seed-coats, which are held down by a special struc- ture hereafter to be described. The movement at right angles to the above lines was due to the arched hypocotyl becoming more arched as it increased in height. The foregoing observa- tions apply to the leg of the arch next to the cotyledons, but

the other leg adjoining the radicle likewise cireumnutated at an equally early age. The movement of the same hypocotyl after it had become straight and vertical, but with the cotyledons only partially expanded, is shown in Fig.29. The course pursued during 12h. apparently represents four and a half ellipses or ovals, with the longer axis of the first at nearly right angles to that of the others. The longer axes of all were oblique to a line joining the opposite cotyledons. The actual extreme distance from side to side over which the summit of the tall hypocotyl passed in the course of 12h, was ‘28 of an inch. The original figure was traced on a large scale, and from the obliquity’ of the line of view the outer parts of the diagram are much exaggerated.

Cotyledons.—On two occasions the movements of the cotyle- dons were traced on a vertical glass, and as the ascending and descending lines did not quite coincide, very narrow ellipses were formed; they therefore circumnutated. Whilst young they rise vertically up at night, but their tips always remain reflexed ; on the following morning they sink down again. With a seedling kept in complete darkness they moved in the same manner, for they sank from 845 a.m. to 4.30 e.m.; they then began to rise and remained clcse together until 10 p.m., when they were last observed. At 7 a.m. on the following morning they were as much expanded as at avy hour on the previous day. The cotyledons of another young seedling, exposed to the light, were fully open for the first time on a certain day, but were found completely closed at 7 a.m. on the following morning. They soon began to expand again, and continued doing so till about 5 p.m.; they then began to rise, and by 10.30 p.m. stood vortically and were almost closed. At 7 a.m. on the third morn- ing they were nearly vertical, and again expanded during the day; on the fourth morning they were not closed, yet they opened a little in the course of the day and rose a little on the folowing night. By this time a minute true leaf had-become developed. Another seedling, still older, bearing a well-developed leaf, had a sharp rigid filament affixed to one of its cotyledons (85 mm. in length), which recorded its own movements on a revolving drum with smoked paper. The observations were made in the hot-house, where the plant had lived, so that there was no change in temperature or light. The record commenced at 11 a.m. on February 18th; and fhom this hour till 3 p.m. the

cotyledon fell; it then rose rapidly till 9 P.m., then very gradually till 3 a.m. February 19th, after which hour it sank gradually till 4.30 p.m.; but the downward movement was inter- rupted by one slight rise or oscillation about 1.30 p.m. After 430 p.m. (19th) the cotyledon rose till 1 a.m. (in the night of February 20th) and then sank very gradually till 9.30 a.m, when our observations ceased. The amount of movement was greater on the 18th than on the 19th or on the morning of the 20th.

Cucurbita aurantia.—An arched hypocotyl was found buried a little beneath the surface of the soil; and in order to prevent it straightening itself quickly, when relieved from the surrounding pressure of the soil, the two legs of the arch were tied together. The seed was then lightly covered with loose damp earth. A filament with a bead at the end was affixed to the basal leg, the movements of which were observed during two days in the usual manner. On the first day the arch moved in a zigzag line towards the side of the basal leg. On the next day, by which time the dependent cotyledons had been dragged above the sur- face of the soil, the tied arch changed its course greatly nine times in the course of 144h. It swept a large, extremely irre- gular, circular figure, returning at night to nearly the same spot whence it had started early in the morning. ‘he line was so strongly zigzag that it apparently represented five ellipses, with their longer axes pointing in various directions. With respect to the periodical movements of the cotyledons, those of several young seedlings formed together at 4 p.m. an angle of about 60°, and at 10 p.m. their lower parts stood vertically and were in contact ; their tips, however, as is usual in the genus, were per- manently reflexed. These cotyledons, at 7 a.m. on the following morning, were again well expanded.

Lagenaria vulgaris (var. miniature Bottle-gourd) (Cucurbi- taceze).— A seedling opened its cotyledons, the movements of which were alone observed, slightly on June 27th, and closed them at night: next day, at noon (28th), they included an angle of 53°, and at 10 r.m. they were in close contact, so that each had risen 263°. At noon, on the 29th, they included an angle of 118°, and at 10 p.m. an angle of 54°, so each had risen 32°. On the following day they were still more open, and the nocturnal rise was greater, but the angles were not measured. Two other seedlings were observed, and behaved during three days in a closely similar manner. The cotyledons, therefore,

open more and more on each succeeding day, and rise each night about 30°; consequently during the first two nights of In order to ascertain more ac- curately the nature of these move- ments, the hypocotyl of a seedling, with its cotyledons well expanded, was secured to a little stick, and a filament with triangles of paper was affixed to one of the cotyledons. The observations were made under a rather dim skylight, and the temperature during the whole time was between 173° to 18° C. (68° to 65° F.). Had the temperature been higher and the light brighter, the movements would probably have

been greater. On July llth (see Fig. 80), the cotyledon fell from 7.35 a.m. till 10 a.m.; it then rose (rapidly after 4 p.m.) till it stood quite vertically at 8.40 r.m. During the early morning of the next day (12th) it fell, and continued to fall till 8 a.m., after which hour it rose, then fell, and again rose, so that by 10.35 p.m. it stood much higher than it did in the morning, but was not vertical as on the preceding night. During the following early morn- ing and whole day (18th) it fell and circumnutated, but had not risen when observed late in the evening ; and this was probably due to the deficiency of heat or light, or of both. We thus see that the coty- ledons became more widely open at noon on each succeeding day; and

Lagenaria vulguris: circumnn- tation of a cotyledon, 13 inch in length, apex only 42 inches from the vertical glass, on which its movements were traced from 7.35 a.m. July 11th to 9.5 a.m. on the 14th. Figure here given reduced to one-third of original scale. that they rose considerably each night, though not acquiring a vertical position, except during the first two nights. Cucumis dudaim (Cucurbitacese).—Two seedlings had opened their cotyledons for the first time during the day,—one to the extent of 90° and the other rather more; they remained in nearly the same position until 10.40 P.m.; but by 7 a.m. on the following morning the one which had been previously open to the extent of 90° had its cotyledons vertical and completely shut; the other seedling had them nearly shut. Later in the morning they opened in the ordinary manner. It appears therefore that the cotyledons of this plant close and open at somewhat different periods from those of the foregoing species of the allied genera of Cucurbita and Lagenaria.

Opuntia basiluris (Cactere).—A seedling was carefully ob- served, because considering its appearance and the nature of the mature plant, it seemed very un- likely that either the liypocotyl or cotyledons would circumnutate to an appreciable extent. The coty- ledons were well developed, being ‘9 of an inch in length, +22 in breadth, and °15 in thickness. The almost cylindrical hypocotyl, now bearing a minute spinous bud Opuntia basilaris: conjoint cir- cumnutation of - hypocotyl and cotyledon; _ filament fixed longitudinally to coty- Iedon, and movement traced during 66 h. on horizontal glass. Movement of the ter- minal bead magnified about 30 times, here reduced to one- thirdscale. Seedling kept in hot-house, feebly illuminated from above,

on its summit, was only ‘45 of an inch in height, and °19 in dia- meter. The tracing (Fig. 31) shows the combined movement of the hypocotyl and of one of the coty- ledons, from 4.45 p.m. on May 28th toll am. onthe 31st. On the 29th a nearly perfect ellipse was com- pleted. On the 30th the hypocotyl moved, from some unknown cause, in the same general direction in a zigzag line; but between 4.30 and 10 p.m. almost completed a second small ellipse. The cotyledons move only a little up and down: thus at 10.15 p.m. they stood only 10° higher than at noon. The chief seat of movement therefore, at least when the cotyledons are rather old as in the present case, lies in the hypocotyl. The ellipse described on the 29th had its longer axis directed at nearly right angles to a line joining the two cotyledons. The actual amount of movement of the bead at the end of the

filament was, as far as could be ascertained, about °14 of an inch. Fietianthus annuus (Composite).—The upper part of the hypocotyl moved during the day-time in the course Mig. 32. shown in the annexed figure (Fig. 32). As the line runs in various directions, cross- ing itself several times, the movement may be con- sidered as one of circumnu- tation. The extreme actual distance travelled was at least ‘1 of an inch. The movements of the cotyle- oe dons of two seedlings were Helianthus annuus : circumnutation of

‘ hypocotyl, with filament fixed across observed; onefacing anorth- ifs summit, traced on a_ horizontal east window, and the other glass in darkness, from 8.45 a.m. to so feebly illuminated from 10-45 ?.3L., and for an hour on follow- : ing morning. Movement of bead above as to be almost in magnified 21 times, here reduced to darkness. They continued — one-half of original scale. to sink till about noon, when they began to rise; but between 5 and 7 or 8 p.m. they either sank a little, or moved laterally, and then again began to rise. At 7 a.m. on the following morning those on the plant before the north-east window had opened so little that they stood at an angle of 73° above the horizon, and were not observed any longer. Those on the seedling which had been kept in almost complete darkness, sank during the whole day, without rising about mid-day, but rose during the night. On the third and fourth days they continued sinking without any alternate ascending movement; and this, no doubt, was due to the absence of light.

Primula Sinensis (Primulacese).—A seedling was placed with the two cotyledons parallel to a north-east window on a day when the light was nearly uniform, and a filament was affixed to one of them. From observations subsequently made on another seedling with the stem secured to a stick, the greater part of the movement shown in the annexed figure (Fig. 33), must have been that of the hypocotyl, though the cotyledons zertainly move up and down to a certain extent both during the day and night. The movements of the same seedling were traced

on the following day with nearly the same result; and there can be no doubt about the cirsumnutation of the hypocotyl. Primula Sinensis: conjoint wrcumnutation of hypocotyl and cotyledon, traced on vertical glass, from 8.40 a.m. to 10.45 P.M. Movements of Cyclamen Persicum (Primulacex).—This plant is generally sup- posed to produce only a single cotyledon, but Dr. H. Gressner * has shown that a second one is developed after a long interval ‘ of time. The hypocotyl is converted into a globular corm, even before the first cotyledon has broken through the ground with its blade closely enfolded and with its petiole in the form of an arch, like the arched hypocotyl or epicotyl-of any ordinary dicotyle- donous plant. A glass filament was affixed to a cotyledon, ‘55 of an inch in height, the petiole of which had straightened itself and stood nearly vertical, but with the blade not as yet fully expanded. Its movements were traced during 243 h. on a horizontal glass, magnified 50 times; and in this interval it described two irregular small \ circles; it therefore circumnu-

Stapelia sarpedon (Ascle- piadex). — This plant, when mature, resembles a cactus. The flattened hypocotyl is fleshy, enlarged in the upper part, and bears two rudimen- tary cotyledons. It breaks vertically to the hypocotyl of a seedling half an inch high; and its movements were traced during 50h. on a horizontal glass (Fig. 34). From some unknown cause it bowed itself to one side, ani as this was effected by a zigzag course, it probably circumnutated; but with hardly any other seedling observed by us was this movement so obscurely shown. —

* Ipomea ceerulea vel Pharbitis nil (Convolvulacese).—Seedlings of this plant were observed because it is a twiner, the upper internodes of which circumnutate conspicuously; but, like other twining plants, the first few internodes which rise above the ground are stiff enough to support themselves, and therefore do not circumnutate in any plainly recognisable manner.* In this particular instance the fifth internode (including the hypo- cotyl) was the first which plainly cireumnutated and twined round a stick. We therefore wished to learn whether circum- nutation could be observed in the hypocotyl if carefully observed in our usual manner. Two seedlings were kept in the dark with filaments fixed to the upper part of their hypocotyls; but from circumstances not worth explaining their movements were traced for only a short time. One moved thrice forwards and twice backwards in nearly opposite directions, in the course of 3h. 15m.; and the other twice forwards and twice backwards in 2h.22m. The hypocotyl therefore circumnutated at a re- markably rapid rate. It may here be added that a filament was affixed transversely to the summit of the second internode above the cotyledons of a little plant 33 inches in height; and its movements were traced ona horizontal glass, It cireumnutated, and the actual distance travelled from side to side was a quarter of an inch, which was too small an amount to be perceived with- out the aid of marks.

The movements of the cotyledons are interesting from their complexity and rapidity, and in some other respects. The hypocotyl (2 inches high) of a vigorous seedling was secured to a stick, and a filament with triangles of paper was affixed to one of the cotyledons. The plant was kept all day in the hot-house, and at 4.20 p.m. (June 20th) was placed under a skylight in the house, and observed occasionally during the evening and night. It fell in a slightly zigzag line to a moderate extent from 4.20 p.m. till 1015 p.m. When looked at shortly after mid- night (12.30 p.m.) it had risen a very little, and considerably by

(pomea cerulea: circumnutation of cotyledon, traced on vertical glass, from 6.10 A.M. June 21st to 6.45 A.M. 22nd. Cotyledon with petiole 1°6 inch in length, apex of blade 4-1 inch from the vertical glass; so movement not greatly mag- nified; temp. 20°C. fallen largely. A new tracing was now begun (see Fig. 35), and soon afterwards, at 6.42 AM., the cotyledon had risen a little. During the forenoon it was observed about every hour; but between 12.30 and 6 p.m. every half-hour. If the observations had been made at these short intervals during the whole day, the figure would have been too intricate to have been copied. As it was, the cotyledon moved up and down in the course of 16h. 20 m. (ie. between 6.10 a.m. and 10.30 p.m.) thirteen times.

The cotyledons of this seed- ling sank downwards during both evenings and the early part of the night, but rose during the latter part. As this is an unusual movement, the cotyledons of twelve other seed- lings were observed ; they stood almost or quite horizontally at mid-day, and at 10 p.m. were all declined at various angles. The most usual angle was be- tween 80° and 35°; but three stood at about 50° and one at even 70° beneath the horizon. The blades of all these cotyle- dons had attained almost their full size, viz. from 1 to 13 inches in length, measured along their midribs. It is a remarkable fact that whilst young—that is, when less than half an inch in length, measured in the same manncr—they do not sink

downwards in the evening. Therefore their weight, which is considerable when almost fully developed, probably came into play in originally determining the downward movement. The periodicity of this movement is much influenced by the degree of light to which the. seedlings have been exposed during the day; for three kept in.an obscure place began to sirk about noon, instead of late in the evening ; anc those of another seed- ling were almost paralysed by having been similarly kept during two whole days. ‘The cotyledons of several other species cf Ipomeea likewise sink downwards late in the evening.

Cerinthe major (Boragines).—The circumnutation of the hypecotyl of a young seedling with the cotyledons hardly Cerinthe major: circumnutation of hypocotyl, with filament fixed across its summit, illuminated from above, traced on horizontal glass, from 9.26 A.M. to 9.53 P.M. on Oct. 25th. Movement of the bead magnified 30 times, here reduced to one-third of original scale. expanded, is shown in the annexed figure (Fig. 36), which apparently represents four or five irregular ellipses, described in the course of a little over 12 hours. Two older seedlings were similarly observed, excepting that one of them was kept in the dark; their hypocotyls also circumnutated, but in a more simple manner. The cotyledons on a seedling exposed to the light fell from the early morning until a little after noon, and then continued to rise until 10.30 p.m. or later. The cotyledons of this same seedling acted in the same general manner during the two following days. It had previously been tried in the dark, and after being thus kept for only 1h. 40 m. the cotyledons began at 4.30 p.m. to sink, instead of continuing to rise till late at night. ae

Nolana prostrata (Nolanee).— The movements were not traced, but a pot with seedlings, which had been kept in the dark for an hour, was placed under the microscope, with the micrometer eye-piece so adjusted that each division equalled séoth of an inch. The apex of one of the cotyledons crossed rather obliquely four divisions in 18 minutes; it was also sink- ing, as shown by getting out of focus. The seedlings were again placed in darkness for another hour, and the apex now

crossed two divisions in 6m. 18s.; that is, at very nearly the Solanum lycoper- sicum: circum nutation of hy- pocotyl, with filament fixed across its sum- mit, traced on horizontal glass, from 10 A.M. to 5 p.m. Oct. 24th. I]]luminated ob- liquely — from above. Move- ment of bead magnified about 35 times, here reduced to one- third of original scale. After another interval of an hour in dark- ness, it crossed two divisions in 4 m. 15s., there- fore at a quicker raie. In the afternoon, after a longer interval in the dark, the apex was motion- less, but after a time it recommenced moving, though slowly; perhaps the room was too cold, Judging from previous cases, there can hardly be a doubt that this seedling was circumnuta- ting.

Solanum lycopersicum (Solaneee) —The move- ments of the hypocotyls of two seedling to- matoes were observed during seven hours, and there could be no doubt that both cireumnu- tated. They were illuminated from above, but by an accident a little light entered on one side, and in the accompanying figure (Fig. 37) it may be seen that the hypocotyl moved to this side (the upper one in the figure), making small loops and zigzagging in its course. The move- ments of the cotyledons were also traced both on vertical and horizontal glasses; their angles with the horizon were likewise measured at various hours. They fell from 8.30 a.m. (October 17th) to about noon; then moved laterally in a zigzag line, and at about 4 P.m. began to rise; they continued to do so until 10.30 p.m, by which hour they stood vertically and were asleep.

At what hour of the night or early morning they began to fall was not ascertained. Owing to the lateral movement shortly after mid-day, the descending and ascending lines did not coincide, and irregular ellipses were described during each 24 h. Lhe regular periodicity of these movements is destroyed, as we shall hereafter see, if the seedlings are kept in the dark. Solanum palinacanthum.—Several arched hypocotyls rising nearly ‘2 of an inch above the ground, but with the cotyledons still buried beneath the surface, were observed, and the tracings showed that they circumnutated. Moreover, in several cases little open circular. spaces or cracks in the argillaceous sand which surrounded the arched hypocotyls were visible, and these appeared to have been made by the hypocotyls having bent first to one and then to another side whilst growing up- wards. In two instances the vertical arches were observed to move to a considerable distance backwards from the point where the cotyledons lay buried; this movement, which has been noticed in some other cases, and which seems to aid in extracting the cotyledons from the buried seed-coats, is due to the com- mencement of the straightening of the hypocotyl. In order to prevent this latter movement, the two legs of an arch, the