The Power of Movement in Plants

the movement of the radicle was magnified by the fila- ment, which was nearly ? inch in length, it was impossible radicle, traced on horizontal glass, from 9 a.m. Jan. 31st to 9 P.M. Feb. 2nd. Movement of bead at end of filament magnified about 40 times. to estimate. Another seed was treated and observed in the same manner, but the radicle in this case protruded ‘1 inch, and was not Brassica oleracea: circumnutating and geotropic movement of radicle, traced on horizontal glass during 46 hours.

fastened so as to project quite vertically upwards. The filament was affixed close to its base. The tracing (Fig. 2, reduced by half) shows the movement from 9am. Jan. 3lst to 7 a.m. Feb. 2nd; but it continued to move during the whole of the Qnd in the same general direction, and in a similar zigzag manner. From the radicle not being quite perpendicular when the filament was affixed geotropism came into play at once; but the irregular zigzag course shows that there was growth (probably preceded by turgescence), sometimes on one and sometimes on another side. Occasionally the bead remained stationary for about an hour, and then probably growth occurred on the side opposite to that which caused the geotropic curva- ture. In the case previously described the basal part of the very short radicle from being turned vertically upwards, was at first very little affected by geotropism. Filaments were affixed in two other instances to rather longer radicles protruding obliquely from seeds which had been turned upside down; and in these cases the lines traced on the horizontal glasses were only slightly zigzag, and the movement was always in the same general direction, through the action of geotropism. All these observations are liable to several causes of error, but we believe, from what will hereafter be shown with respect to the move- ments of the radicles of other plants, that they may be largely trusted.

Hypocotyl.—The hypocotyl protrudes through the seed-coats as a rectangular projection, which grows rapidly into an arch like the letter U turned upside down q; the cotyledons being still enclosed within the seed. In whatever position the seed may be embedded in the earth or otherwise fixed, both legs of the arch bend upwards through apogeotropism, and thus rise vertically above the ground. As soon as this has taken place, or even earlier, the inner or concave surface of the arch grows more quickly than the upper or convex surface; and this tends to separate the two legs and aids in drawing the cotyledons out of the buried seed-coats. By the growth of the whole arch the cotyledons are ultimately dragged from beneath the ground, even from a considerable depth; and now the hypocotyl quickly straightens itself by the incrersed growth of the concave side.

Even whilst the arched or doubled hypocotyl is still beneath the ground, it circumnutates as much as the pressure of the sur- rounding soil will permit; but this was difficult to observe, because as soon as the arch is freed from lateral pressure the two legs begin to separate, even at a very early age, before the arch would naturally have reached the surface. Seeds were allowed to germinate on the surface of damp earth, and after they had fixed themselves by their radicles, and after the, as yet, only

slightly arched hypocotyl had become nearly vertical, a glass filament was affixed on two occasions near to the base of the basal leg (i.e. the one in connection with the radicle), and its movements were traced in darkness on a horizontal glass. The result was that long lines were formed running in nearly the plane of the vertical arch, due to the early separation of the two legs now freed from pressure; but as the lines were zigzag, showing lateral movement, the arch must have been circum- nutating, whilst it was straightening itself by growth along its inner or concave surface.

A somewhat different method of observation was next followed: Brassica oleracea: circumnutating movement of buried and arched hypo- cotyl (dimly illuminated from above), traced on horizontal glass during 45 hours. Movement of bead of filament magnified about 25 times, and here reduced to one-half of original scale. as soon as the earth with seeds in a pot began to crack, the surface was removed in parts to the depth of ‘2 inch; and a filament was fixed to the basal leg of a buried and arched hypo- cotyl, just above the summit of the radicle. The cotyledons were still almost completely enclosed within the much-cracked seed-coats; and these were again covered up with damp adhesive soil pressed pretty firmly down. The movement of the filament was traced (Fig. 3) from 11 a.m. Feb. 5th till 8 a.m. Feb. 7th. By this latter period the cotyledons had been dragged from beneath the pressed-down earth, but the upper part of the hypocotyl still formed nearly a right angle with the lower part. The tracing sLows that the arched hypocotyl tends at this early

age to circumnutate irregularly. On the first day the greater movement (from right to left in the figure) was not in the plane of the vertical and arched hypocotyl, but at right angles to it, or in the plane of the two cotyledons, which were still in close contact. The basal leg of the arch at the time when the filament was affixed to it, was already bowed considerably backwards, or from the cotyledons; had the filament been affixed before this bowing occurred, the chief movement would have been at right angles to that shown in the figure. A filament was attached to another buried hypocotyl of the same age, and it moved in a similar general manner, but the line traced was not so complex. This hypocotyl became almost straight, and the cotyledons were dragged from beneath the ground on theevening of the second day

Brassica oleracea: circumnutating movement of buried and arched hypo- cotyl, with the two legs of the arch tied together, traced on horizontal glass during 33} hours. Movement of the bead of filament magnified about 26 times, and here reduzed to one-half original scale. Before the above observations were made, some arched hypo- cotyls buried at the depth of a quarter of an inch were un- covered; and in order to prevent the two legs of the arch from beginning to separate at once, they were tied together with fine silk. This was done partly because we wished to ascertain how long the hypocotyl, in its arched condition, would continue to move, and whether the movement when not masked and disturbed by the straightening process, indicated circumnu- tation. Firstly, a filament was fixed to the basal leg of an arched hypocotyl close above the summit of the radicle. The cotyledons were still partially enclosed within the seed-coats, The movement was traced (Fig. 4) from 9.20 am. on Dee,

23rd to 6.45 a.m. on Dec. 25th. No doubt the natural move- ment was much disturbed by the two legs having been tied together; but we see that it was distinctly zigzag, first in one direction and then in an almost opposite one. After 3 P.M. on the 24th the arched hypocotyl sometimes remained stationary for a considerable time, and when moving, moved far slower than before. Therefore, on the morning of the 25th, the glass fila- ment was removed from the base of the basal leg, and was fixed horizontally on the summit of the arch, which, from the legs having been tied, had grown broad and almost flat. The movement was now traced during 23 hours (Fig. 5), and we

Brassica oleracea: circumtutating movement of the crown of a buried and arched hypocotyl, with the two legs tied together, traced on a hori- zontal glass during 23 hours, Movement of the bead of the filament magnified about 58 times, and here reduced to one-half original scale. see that the course was still zigzag, which indicates a tendency to circumnutation. The base of the basal leg by this time had almost completely ceased to move. As soon as the cotyledons have been naturally dragged from beneath the ground, and the hypocotyl has straightened itself by growth along the inner or concave surface, there is nothing to interfere with the free movements of the parts; and the circum- nutation now becomes much more regular and clearly displayed, as shown in the following cases:—A seedling was placed in front and near a north-east window with a line joining the

two cotyledons parallel to the window. It was thus left the whole day so as to accommodate itself to the light. On the following morning a filament was fixed to the midrib of the larger and taller cotyledon (which enfolds the other and smaller one, whilst still within the seed), and a mark being placed close behind, the movement of the whole plant, that is, of the hypocotyl and cotyledon, was traced greatly magnified on a ver- tical glass. At first the plant bent so much towards the light that it was useless to attempt to trace the movement ; but at 10 a.m. heliotropism almost wholly ceased and tho first dot was

Brassica oleracea: conjoint circumnutation of the hypocotyl and eotyledona during 10 hours 45 minutes. Figure here reduced to one-half original scale. made on the glass. The last was made at 8.45 p.m.; seventeen dots being altogether made in this interval of 10h. 45 m. (see Fig. 6). It should be noticed that when I looked shortly after 4p.u. the bead was pointing off the glass, but it came on again at 5.30 p.m., and the course during this interval of 1h. 830m. has been filled up by imagination, but cannot be far from correct The bead moved seven times from side to side, and thus de- scribed 33 ellipses in 102 h.; each being completed on an average in 3h.4m.

On the previous day anothcr seedling had been observed under similar conditions, excepting that the plant was so placed that a line joining the two cotyledons pointed towards the window ; and the filament was attached to the smaller coty- ledon on the side furthest from the window. Moreover, the plant was now for the first time placed in this position. Tho cotyledons bowed themselves greatly towards the light from 8 to 10.50 a.m, when the first dot was made (Fig. 7). During the

Brassica oleracea : conjoint circumnutation of the hypocotyl and cotyledons, from 10.50 a.m. to 8 A.M. on the following morning. Tracing made ou a vertical glass, next 12 hours the bead swept obliquely up and down 8 times and described 4 figures representing ellipses; so that it travelled at nearly the same rate as in the previous case. During the night it moved upwards, owing to the sleep-movement of the cotyledons, and continued to move in the same direction till 9am. on the following morning; but this latter movement would not have occurred with seedlings under their natural conditions fully exposed to the light.

begun to fall, and a dot was made on a fresh glass. The move- ment was traced until 5.30 p.m. as shown in (Fig. 8), which is given, because the course followed was much more irregular than on the two previous Fig. 8. occasions. During these 8 hours the bead changed its course greatly 10 times. The upward movement of the cotyledon during the afternoon and early part of the night is here plainly shown. As the filaments were fixed in the three last cases to one of the coty- ledons, and as the hypo- cotyl was left free, the tracings show the move-

Brassica oleracea: conjoint circumnutation ment of both organs con- of the hypocotyl and cotyledons during joined; and we now 8 hours. Figure here reduced to one- wished to ascertain whe- third of the original scale, as traced on hey both circumnutated. vertical glass, ‘i Filaments were therefore fixed horizontally to two hypocotyls close beneath the petioles of their cotyledons. These seedlings had stood for two days in the same position before a north-east window. In the morn- ing, up to about 11 am., they moved in zigzag lines towards the light; and at night they again became almost upright through apogeotropism. After about 11 a.m. they moved a little back from the light, often crossing and recrossing their former path in zigzag lines. The sky on this day varied much in brightness, and these observations merely proved that the hypocotyls were continually moving in a manner resembling circumnutation. On a previous day which was uniformly cloudy, a hypocotyl was firmly secured to a little stick, and a filament was fixed to the larger of the two cotyledons, and its movement was traced on a vertical glass. It fell greatly from 8.52 a.m., when the first dot was made, till 10.55 a.m.; it then rose greatly until 12.17p.m. Afterwards it fell a little and madea loop, but by 2.22 p.m. it had risen a little and continued rising till 9.23 p.m., when it made another loop, and at 10.30 p.m. was again rising. These observations show that the cotyledons move

vertically up and down all day long, and as there was some slight lateral movement, they circumnutated. The cabbage was one of the first plants, the seedlings of which were observed by us, and we did not then know how far the circumnutation of the different parts was affected by light. Young seedlings were therefore kept in com- plete darkness except for a minute or two during each observation, when they were illuminated by a small wax taper held almost vertically above them. During the first day the hypocotyl of one changed its course 18 times (see Fig. 9); and it deserves notice that the longer axes of the figures described often cross one another at right or nearly right angles. Another seedling was observed in the same manner, but it was much older, for it had formed a true leaf a quarter of an inch in length, and the hy- pocotyl was 18 inch in height. The figure traced was a very complex one, though the movement was not so great in extent as in the last case. The hypocotyl of another seedling of the same age was secured to a little stick, and a filament having been fixed to the midrib of one of the cotyledons, the movement of

Brassica oleracea: circumnutation of hypocotyl, in darkness, traced on a horizontal glass, by means of a fila- ment with a bead fixed across its summit, between 9.15 a.m. and 8.30 a.m. on the following morn- ing. Figure here reduced to one- half of original scale, the bead was traced during 14h. 15m. (see Fig. 10) in darkness. It should be noted that the chief movement of the cotyledons, namely, up and down, would be shown on a horizontal glass- plate only by the lines in the direction of the midrib (that is,

up and down, as Fig. 10 here stands) being a little lengthened or shortened; whereas any -lateral movement would be well exhibited. The present tracing shows Fig. 10. that the cotyledon did thus move laterally (that is, from side to side in the tracing) 12 times in the 14 h. 15 m. of observa- tion. Therefore the cotyledons certainly circumnutated, though the chief move- ment was up and down in a vertical plane. Rate of movement.—The movements of the hypocotyls and cotyledons of seedling cabbages of different ages have now been sufficiently illustrated. With respect to the rate, seedlings were placed under the

Brassica oleracea: cit- microscope with the stage removed, and cumnutation of a 3 : 5 ‘ cotyledon, the hypo- With a micrometer eye-piece so adjusted cotyl having been that each division equalled =4, inch; the secured to a‘stick, plants were illuminated by light passing paren TaN through a solution of bichromate of potas- tal glass, in dark- * mega : a ness, from 8.15 a.m. Sium so as to eliminate hceliotropism. to 10.30 P.M. Move- Under these circumstances it was interest- ayia ae ing to observe how rapidly the circum- fied 13 times. nutating apex of a cotyledon passed across

the divisions of the micrometer. Whilst travelling in any direction the apex generally oscillated back- wards and forwards to the extent of =35 and sometimes of nearly zig Of aninch. These oscillations were quite different from the trembling caused by any disturbance in the same room or by the shutting of a distant door. The first seedling observed was nearly two inches in height and had been etiolated by having been grown in darkness. The tip of the cotyledon passed across

10 divisions of the micrometer, that is, 7, of an inch, in 6 m. 40 s. Short glass filaments were then fixed vertically to the hypocotyls of several seedlings so as to project a little above the cotyledons, thus exaggerating the rate of movement; but only a few of the observations thus made are worth giving. The most remarkable fact was the oscillatory movement above described, and the difference of rate at which the point crossed the divi- sions of the micrometer, after short intervals of time. For instance, a tall not-etiolated seedling had been kept for 14 h. in darkness; it was exposed before a north-east window for only

two or three minutes whilst a glass filament was fixed vertically to the hypocotyl; it was then again placed in darkness for half an hour and afterwards observed by light passing through bichromate of potassium. The point, oscillating as usual, crossed five divisions of the micrometer (i.e. 735 inch) in lm. 30s. The seedling was then left in darkness for an hour, and now it required 3m. 6s. to cross one division, that is, 15 m. 80s. to have crossed five divisions. Another seedling, after being occasionally observed in the back part of a northern room with a very dull light, and left in complete darkness for intervals of half an hour, crossed five divisions in 5m. in the direction of the window, so that we concluded that the move- ment was heliotropic. But this was probably not the case, for it was placed close to a north-east window and left there for 25 m., after which time, instead of moving still more quickly towards the light, as might have been expected, it travelled only at the rate of 12m. 30s. for five divisions. It was then again left in complete darkness for 1h., and the point now travelled in the same direction as before, but at the rate of 3m. 18s. for five divisions.

_ We shall have to recur to the cotyledons of the cabbage in a future chapter, when we treat of their sleep-movements. The circumnutation, also, of the leaves of fully-developed plants will hereafter be described. Githago segetum: circumnutation of hypocotyl, traced on a horizontal glass, by means of a filament fixed transversely across its summit, from 8.15 A.M. to 12.15 P.M. on the following day. Movement of bead of filament magnified about 13 times, here reduced to one-half the original scale.

Githago segetum (Caryophyllese).—A young seedling was dimly Uluminated from above, and the circumnutation of the hypo- 22, Cuar. 1 cotyl was observed during 28 h., as shown in Fig. 11. It moved in all directions; the lines from right and to left in the figure being parallel to the blades of the cotyledons. The actual distance travelled from side to side by the summit of the hypocotyl was about 2 of an inch; but it was impossible to be accurate on this head, as the more obliquely the plant was viewed, after it had moved for some time, the more the distances were exaggerated.

We endeavoured to observe the circumnutation of the coty- ledons, but as they close together unless kept exposed to a mode- rately bright light, and as the hypocotyl is extremely heliotropic, the necessary arrangements were too troublesome. We shall recur to the noc- turnal or sleep-movements of the cotyle- dons in a future chapter. £o Gossypium (var. Nankin cotton) (Mal- vaces).—The circumnutation of a hypo- cotyl was observed in the hot-house, but the movement was so much exaggerated

tation of hypocotyl, traced on a horizon- tal glass, from 10.30 AM. to 9.30 a.M. on following morning, by means of a fila- ment fixed across its summit. Move- ment of bead of fila- ment magnified about twice; seedling illu- minated from above. that the bead twice passed for a time out of view. Itwas, however, manifest that two somewhat irregular ellipses were nearly completed in 9 h. Another seedling, 12 in. in height, was then observed during 23h.; but the observations were not made at sufficiently short intervals, as shown by the few dots in Fig. 12, and the tracing was not now sufficiently enlarged.

Nevertheless there could be no doubt about the circumnutation of the hypocotyl, which described in 12h. a figure representing thrce irregular ellipses of unequal sizes, The cotyledons are in constant movement up and down during the whole day, and as they offer the unusual case of moving downwards late in the evening and in the early part of the night, many observations were made on them. A filament was fixed along the middle of one, and its movement traced on a vertical glass; but the tracing is not given, as the hypocotyl was not secured, so that it was impossible to distinguish clearly between its movement and that of the cotyledon. The coty- ledons rose from 10.30 a.m. to about 3 p.x. ; they then sank till 10 p.am., rising, however, greatly in the latter part of the night

The angles above the horizon at which the cotyledons of another seedling stood at different hours is recorded in the following short table :— The position of the two cotyledons was roughly sketched at various hours with the same general result. In the following summer, the hypocotyl of a fourth seedling was secured to a little stick, and a glass filament with triangles of paper having been fixed to one of the cotyledons, its move- ments were traced on a vertical glass under a double skylight in the house. The first dot was made at 4.20 p.m. June 20th; and the cotyledon fell till 10.15 p.m. in a nearly straight line. Just past midnight it was found a little lower and somewhat to one side. By the early morning, at 3.45 a.m., it had risen greatly, but by 6.20 a.m. had fallen a little. During the whole of this day (21st) it fell in a slightly zigzag line, but its normal course was disturbed by the want of sufficient illumination, for during the night it rose only a little, and travelled irregularly during the whole of the following day and night of June 22nd. The ascending and descending lines traced during the three days did not coincide, so that the movement was one of circumnuta- tion. This seedling was then taken back to the hot-house, and after five days was inspected at 10 p.m., when the cotyledons were found hanging so nearly vertically down, that they might justly be said to have been asleep. On the following morning they had resumed their usual horizontal position.

Ozxalis rosea (Oxalidese).—The hypocotyl was secured to a little stick, and an extremely thin glass filament, with two triangles of paper, was attached to one of the cotyledons, which was ‘15 irch in length. In this and the following species the end of the petiole, where united to the blade, is developed into a pulvinus. The apex of the cotyledon stood only 5 inches from the vertical glass, so that its movement was not greatly exaggerated as long as it remained nearly horizontal; but in the course of the day it both rose considerably above and fell beneath a horizontal posi- tion, and then of course the movement was much exaggerated.