The Power of Movement in Plants

respect to the sleep of cotyledons. In certain cases, the cotyledons whilst young diverge during the day to only a very moderate extent, so that a small rise at night, which we know occurs with the cotyledons of many plants, would necessarily cause them to assume a vertical or nearly vertical position at night; and in this case it would be rash to infer that the movement was effected for any special purpose. On this account we hesitated long whether we should introduce several Cucurbitaceous plants into the following list; but from reasons, presently to be given, we thought that they had better be at least temporarily included. This same source of doubt applies in some few other cases ; for at the commencement of our observations we did not always attend sufficiently to whether the cotyle- dons stood nearly horizontally in the middle of the day. With several seedlings, the cotyledons assume a highly inclined position at night during so short a period of their life, that a doubt naturally arises whether this can be of any service to the plant. Nevertheless, in most of the cases given in the following list, the coty- ledons may be as certainly said to sleep as may the leaves of any plant. In two cases, namely, with the cabbage and radish, the cotyledons of which rise almost vertically during the few first nights of their life, it was ascertained by placing young seedlings in the klinostat, that the upward movement was not due to apogeotropism.

The names of the plants, the cotyledons of which stand at night at an angle of at least 60° with the horizon, are arranged in the appended list on the same system as previously followed. The numbers of the Families, and with the Leguminose the numbers of the Tribes, have been added to show how widely the plants in question are distributed throughout the be made about many of the plants in the list. In doing so, it will be convenient not to follow strictly any systematic order, but to treat of the Oxalide and the Leguminose at the close; for in these two Families the cotyledons are generally provided with a pulvinus, and their movements endure for a much longer time than those of the other plants in

List of Seedling Plants, the cotyledons of which rise or sink at night to an angle of at least 60° above or beneath the horizon. Stellaria media (according to Hof- meister, as quoted), Caryophyl- ex Anoda Wrightii. Malvacee (Fam. Gossypium (var. Nankin cotton). Malvacer, Oxalis rosea. Oxalide (Fam. 41). — floribunda. - articulata. Valdiviana, sensitiva. Geranium rotundifolium. niacez (Fam. 47). Trifolium subterrancum. Legu- minose (Fam. 75, Tribe 3). strictum, leucanthemum. Lotus ornithopopoides, nose (Tribe 4), peregrinus, Jacobxus. Clianthus Dampieri. Legumi- nos: (Tribe 5)—according to M. Ramey. Smithia — sensitiva. (Tribe 6). Hematoxylon Campechianum. Le-

Mimulus, (sp. ?) Scrophularinea (Fam. 159) — from information given us by Prof. Pfetler. Amaranthus caudatus. Amaran- thacea (Fam. 180). Cannabis sativa (?). Cannabince Brassica oleracea (Cruciferee). —1t was shown in the first chapter that the cotyledons of the common cabbage rise in the evening and stand vertically up at night with their petioles in contact. But as the two cotyledons are of unequal height, they frequently interfere a little with each other’s movements, the shorter one often not standing quite vertically. They awake early in the morning; thus at 645 am. on Nov. 27th, whilst it was still dark, the cotyledons, which had been vertical and in contact on the previous evening, were reflexed, and thus presented a very different appearance. It should he borne in mind that seedlings in germinating at the proper season, would not be subjected to darkness at this hour in the morning. The above amount of movement of the cotyledons is only temporary, lasting with plants kept in a warm greenhouse from four to six days; how long it would last with seedlings growing out of doors we do not know.

Raphanus sativus.—In the middle of the day the blades of the cotyledons of 10 seedlings stood at right angles to their hypocotyls, with their petioles a little divergent; at night the blades stood vertically, with their bases in contact and with their petioles parallel. Next morning, at 6.45 4.m., whilst it was still dark, the blades were horizontal. On the following night they were much raised, but hardly stood sufficiently ver- tical to be said to be asleep, and so it was in a still less degree on the third night. Therefore the cotyledons of this plant (kept in the greenhouse) go to sleep for even a shorter time than those of the cabbage. Similar observations were made, but only during a single day and night, on 18 other seedlings likewise raised in the greenhouse, with the same result.

The petioles of the cotyledons of 11 young scedlings of Sinupis nigra were slightly divergent at noon, and the blades stood at right angles to the hypocotyls; at night the pctioles were in close contact, and the blades considerably raised, with their bases in contact, but only a few stood sufficiently apright to be called asleep. On the following morning, 302 MODIFIED CIRCUMNUTATION. Cuar. V1. the petioles diverged before it was light. The hypocotyl a slightly sensitive, so that if rubbed with a needle it bends towards the rubbed side. In the case of Lepidiwm sativum, the petioles of the cotyledons of young seedlings diverse during the day and converge so as to touch each other during the night, by which means the bases of the tripartite blades are brought into contact; but the blades are so little raised that they cannot be said to sleep. The cotyledons of several other cruciferous plants were observed, but they did not rise sufficiently during the night to be said to sleep.

Githago segetum (Caryophyllez).—On the first day after the cotyledons had burst through the seed-coats, they stood at noon at an angle of 75° above the horizon; at night they moved upwards, each through an angle of 15° so as to stand quite vertical and in contact with one another. On the second day they stood at noon at 59° above the horizon, and again at night were completely closed, each having risen 31°. On the fourth day the cotyledons did not quite close at night. The first and succeeding pairs of young true leaves behaved in exactly the same manner. We think that the movement in this case may be called nyctitropic, though the angle passed through was small. The cotyledons are very sensitive to light and will not expand if exposed to an extremcly dim one.

Anodu Wrightii (Malvace).—The cotyledons whilst moderately young, and only from ‘2 to ‘3 inch in diameter, sink in the evening from their mid-day horizontal position to about 35° beneath the horizon. But when the same seedlings were older and had produced small true leaves, the almost orbicular cotyledons, now ‘55 inch in diameter, moved vertically downwards at night. This fact made us suspect that their sinking might be due merely to their weight; but they were not in the least flaccid, and when lifted up sprang back through elasticity into their former dependent position. A pot with some old seedlings was turned upside down in the afternoon, before the noc- turnal fall had commenced, and at night they assumed in op- position to their own weight (and to any geotropie action) an upwardly directed vertical position. When pots were thus reversed, after the evening fall had already commenced, the sinking movement appeared to be somewhat disturbed; but all their movements were occasionally variable without any apparent cause. is latter fact, as well as that of the young cotyledons uot sinking nearly so much as the older ones, deserves notice.

Although the movement of the cotyledons endured for a long time, no pulvinus was exteriorly visible; but their growth continued for a long time. The cotyledons appear to be only slightly heliotropic, though the hypocotyl is strongly go. Gossypium arborcum (?) (var. Naukin cotton) (Malvacer).—Tie cotyleunus behave in nearly the same manner as those of the Anoda, On June 15th the cotyledons of two seedlings were ‘65 inch in length (measured along the midrib) and stood hori- zontally at noon; at 10 P.M. they occupied the same position and had not fallen at all. .On June 23rd, the cotyledons of one of these seedlings were 11 inch in length, and by 10 p.m. they had fallen from a horizontal position to 62° beneath the horizon, The cotyledons of the other seedling were 13 inch in length, aud a minute true leaf had been formed; they had fallen at 10 p.m. to 70° beneath the horizon. On June 24th, the true leaf of this latter seedling was 9 inch in length, and the cotyledons occu- picd nearly the same position at night. By July 9th the cctyle- dons appeared very old and showed signs of withering; but they stood at noon almost horizontally, aud at 10 p.m. hung down vertically.

Gossypium herbi ceum.—It is remarkable that the cotyledons of this species behave differently from those of the last. They were observed durivg 6 weeks from their first development until they had grown to a very large size (still appearing fresh and green), viz. 24 inches in breadth. At this age a true leaf had been formed, which with its petiole was 2 inches long. During the whole of these 6 weeks the cotyledons did not sink at night ; yet when old their weight was considerable and they were borne by much elongated petioles. Seedlings raised from some seed sent us from Naples, behaved in the same manner ; as did those of a kind cultivated in Alabama and cf the Sea-island cotton. To what species these three latter forms belong we do not know. We could not make out in the case of the Naples cotton, that the position of the cotyledons at night was influenced by the soil being more or less dry; care being taken that they were not rendered flaccid by being too dry. The weight of the large cotyledons of the Alabama and Sea-island kinds caused them to hang somewhat dcwnwards, when the pots in which they grew were left for a time upside down. It should, however, be observed that these three kinds were raised in the middle of the winter, which sometimes greatly interferes with the proper nyctitropic movements of leaves and cotyledons.

Cucurbitacece—The cotyledons of Cucurbita aurantia and ovi- fera, and of Lagenaria vulgaris, stand from the Ist to the 3rd day of their life at about 60° above the horizon, and at night rise up so as to become vertical and in close contact with one another. With Cucumis dudaim they stood at noon at 45° above the hori- zon, and closed at night. The tips of the cotyledons of all these species are, however, reflexed, so that this part is fully exposed to the zenith at night; and this fact is opposed to the belief that the movement is of the same nature as that of sleeping plants. After the first two or three days the cotyledons diverge more during the day and cease to close at night. Those of T'richosanthes anguina are somewhat thick and fleshy, and did not rise at night; and they could perhaps hardly be expected to do so. On the other hand, those of Acanthosicyos horridu* present nothing in their appearance opposed to their moving at night in the same manner as the preceding species ; yet they did not rise up in any plain manner. This fact leads to the belief that the nocturnal movements of the above-named species has been acquired for some special purpose, which may be to protect the young plumule from radiation, by the close contact of the whole basal portion of the two cotyledons.

Geranium rotundi/olium (Geraniacer).—A single seedling came up accidentally in a pot, and its cotyledons were observed to bend perpendicularly downwards during several successive nights, having been horizontal at noon. It grew into a fine plant but died before flowering: it was sent to Kew and pro- nounced to be certainly a Geranium, and in all probability the above-named species. This case is remarkable because the cotyledons of G. cinereum, Endressii, Ibericum, Richardsont, and subcuulescens were observed during some wecks in the winter, and they did not sink, whilst those of G. Jb.ricum rose 27° at night.

Apium petroselinum (Umbcllifere).—A seedling had its coty- ledons (Nov. 22nd) almost fully expanded during the day; by 8.30 p.m. they had risen considerably, and at 10.380 P.a. were almost closed, their tips being only ;8; of an inch apart. On the following morning (23rd) the tips were 338, of an inch apart, * This plant, from Dammara_ climber; it has been deacribed Land in S. Africa, is remarkable in ‘Transact. Linn. Soc.,’ xxvii from being the one known mem- _ p, 30. ber of the Family which is not a

or more than seven times as much. On the next night the cotyledons occupied nearly the same position as before. On the morning of the 24th they stood horizontally, and at night were 60° above the horizon ; and so it was on the night of the 25th. But four days afterwards (on the 29th), when the seedlings were a week old, the cotyledons had ceased to rise at night to any plain degree. Apium graveolens.—The cotyledons at noon were horizontal, and at 10 p.m. stood at an angle of 61° above the horizon.

Lactuca scarivla (Composite).—The cotyledons whilst young stood sub-horizontally during the day, and at night rose so as to be almost vertical, and some were quite vertical and closed ; but this movement ceased when they had grown old and large, after an interval of 11 days. Helianthus annwus (Composite).—This case is rather doubtful ; the cotyledons rise at night, and on one occasion they stood at 73° above the horizon, so that they might then be said to have been asleep.

Ipomea cerulea vel Pharbitis nil (Convolvulacese).—The coty- ledons behave in nearly the same manner as those of the Anocla and Nankin cotton, and like them grow to a large size. Whilst young and small, so that their blades were from ‘5 to ‘6 of an inch in length, measured along the middle to the base of the central notch, they remained horizontal both during the middle of the day and at night. As they increased in size they began to sink more and more in the evening and early night; and when they had grown to a length (measured in the above manner) of from | to 1:25 inch, they sank between 55° and 70° beneath the horizon. They acted, however, in this manner only when they had been well illuminated during the day. Never- theless, the cotyledons have little or no power of bending towards a lateral light, although the hypocotyl] is strongly helio- tropic. They are not provided with a pulvinus, but continue to grow for a long time.

Ipomea purpurea (vel Pharbitis hispita)—The cotyledons behave in all respects like those of I. cerulea. A seedling with cotyledons ‘75 inch in length (measured as before) and 1:65 inch in breadth, having a small true leaf developed, was placed at 5.30 p.m. on a klinostat in a darkened box, so that neither weight nor geotropism could act on them. At 10 p.m. one coty- Jedon stood at 77° and the other at 82° beneath the horizon. Before being placed in tho klinostat they stood at 15° and 29°

beneath the horizon. The nocturnal position depends chiefly on the curvature of the petiole close to the blade, but the whole petiole becomes slightly curved downwards. It deserves notice that seedlings of this and the last-named species were raised at the end of February and another lot in the middle of March, and the cotyledons in neither case exhibited any nyctitropic movement. Ipomaa bona-nox.—The cotyledons after a few days grow to an enormous size, those on a young seedling being 3; inches in breadth. They were extended horizontally at noon, and at 10 pm. stood at 63° beneath the horizon. Five days after- wards they were 4} inches in breadth, and at night one stood at 64° and the other 48° beneath the horizon. Though the blades are thin, yet from their great size and from the petioles being long, we imagined that their depression at night might be determined by their weight; but when the pot was laid hori- zontally, they became curved towards the hypocotyl, which movement-could not have been in the least aided by their weight, at the same time they were somewhat twisted upwards through apogeotropism. Nevertheless, the weight of the coty- ledons is so far influential, that when on another night the pot was turned upside down, they were unable to rise and thus to assume their proper nocturnal position.

Ipom+a coccinea.—The cotyledons whilst young do not sink at night, but when grown a little older, but still only ‘4 inch in length (measured as before) and ‘82 in breadth, they became greatly depressed. In one case they were horizontal at noon, and at 10 p.xt. one of them stood at 64° and the other at 47° beneath the horizon. The blades are thin, and the petioles, which become much curved down at night, are short, so that here weight can hardly have produced any effect. With all the above species of Ipomcea, when the two cotyledons on the same seedling were unequally depressed at night, this seemed to depend on the position which they had held during the day with reference to the light.

Solanum lycopersicum (Solanew).— The cotyledons rise soe much at night as to come nearly in contact. Those of S. palina- canthum were horizontal at noon, and by 10 p.m. had risen only 27° 80'; but on the fullowing morning before it was light they stood at 59° above the horizon, aud in the afternoon of the same diy were again horizontal. The behaviour of the cotyledons of this latter species seems, therefore, to be anomalous. Mirabilis julapa and longiflora (Nyctagines).— The cotyledons, which are of unequal size, stand horizontally during the middle of the day, and at night rise up vertically and come into close contact with oneanother. But this movement with J. longijlora lasted for only the three first nights.

Betu vulgaris (Polygonese).—A large number of seedlings were observed on three occasions. During the day the cotyledons sometimes stood sub-horizontally, but more commonly at an angle of about 50° above the horizon, and for the first two or three nights they rose up vertically so as to be completely closed. During the succeeding one or two nights they rose only a little, and afterwards hardly at all. Amaranthus cuudatus (Amaranthacese)—At noon the coty- ledons of many seedlings, which had just germinated, stood at about 45° above the horizon, and at 10.15 p.m. some were nearly and others quite closed. On the following morning they were again well expanded or open.

Cunnabis sativa (Cannabine).— We are very doubtful whether this plant ought to be hereincluded. The cotyledons of a large number of seedlings, after being well illuminated during the day, were curved downwards at night, so that the tips of some pointed directly to the ground, but the basal part did not appear to be at all depressed. On the following morning they were again flat and horizontal. The cotyledons of many other seed- lings were at the same time not in any way affected. Therefore this case seems very different from that of ordinary sleep, and probably comes under the head of epinasty, as is the case with the leaves of this plant according to Kraus. The cotyledons are heliotropic, and so is the hypocotyl in a still stronger degree,

Oxalis—We now come to cotyledons provided with a pulvinus, all of which are remarkable from the continuance of the nocturnal movements during several days or even weeks, and apparently after growth has ceased. The cotyledons of O. rosea, floribunda and «rticulata sink vertically down at night and clasp the upper part of the hypocotyl. Those of 0. Vuléiviuna and sensitiva, on the contrary, rise vertically up, so that their upper surfaces come into close contact; and after the young leaves are developed these are clasped by the cotyledons. Asin the daytime they stand hori- zontally, or are even a little deflected beneath the horizon, they move in the evening through an angle of at least 90° Their somplicated circumnutating movements during the day have

been described in the first chapter. The experiment was a superfluous one, but pots with seedlings of O. rosea and floribunda were turned upside down, as soon as the cotyledons began to show any signs of sleep, and this made no difference in their movements. Leguminose.—It may be seen in our list that the cotyledons of several species in nine genera, widcly distributed through- out the Family, sleep at night; and this probably is the case with many others. ‘lhe cotyledons of all these species are pro- vided with a pulvinus; and the movement in all is continued during many days or weeks. In Cassia the cotyledons of the ten species in the list rise up vertically at night and come into close contact with one another. We observed that those of C. florida opened in the morning rather later than those of C. glauca and pubescens. The movement is exactly the same in (. mimosoides as in the other species, though its subsequentl7 developed leaves sleep in a different manner. The cotyledons of an eleventh species, namely, C. nodosa, are thick and fleshy, and do not rise up at night. The circumnutation of the coty- ledons during the day of C. tora has been described in the first chapter. Although the cotyledons of Smithia sensitiva rose from a horizontal position in the middle of the day to a vertical one at night, those of S. Pfundii, which are thick and fleshy, did not sleep. When Mimusa pudica and albida have been kept at a sufficiently high temperature during the day, the cotyledons come into close contact at night ; otherwise they merely rise up almost vertically. The circumnutation of those of M. pudica has been described. The cotylclons of a Bauhinia from St. Catharina in Brazil stood during the day at an angle of about 5u° above the horizon, and at night rose to 77°; but it is pro- bable that they would have closed completely, if the seedlings had heen kept in a warmer place.

Lotus.—In three species of Lotus the cotyledons were observed to sleep. Those of L. Jacobeus present the singular case of not rising at night in any conspicuous manner for the first 5 or 6 days of their life, and the pulvinus is not well developed at this period. Afterwards the sleeping movement is well dis- played, though to a variable degree, and is long continued. We shall hereafter meet with a nearly parallel case with the leaves of Sida rhombifuliu, The cotyledons of L. Gebelii are only slightly raised at night, and differ much in this respect frum the three species in cur list.

Prifoliwm—tThe germination of 21 species was observed. In most of them the cotyledons rise hardly at all, or only slightly. at night; but those of 7. glomeratum, striatum and incainatum rose from 45° to 55° above the horizon. With 7. subterraneum, leucanthemum and strictum, they stood up vertically; and with T. strictum the rising;movement is accompanied, as we skall see, by another movement, which makes us believe that the rising is truly nyctitropic. We did not carefully examine the coty- ledons of all the species for a pulvinus, but this organ was distinctly present in those of 7. subterranewm and striclwm ; whilst, there was no trace of a pulvinus in some species, for instance, in L. resupinatum, the cotyledons of which do not rise at night.

Trifolium subterrancum.—The blades of the cotyledons on the first day after germination (Nov. 21st) were not fully expanded, being inclined at about 35° above the horizon; at night they rose to about 75°. Two days afterwards the blades at noon were horizontal, with the petioles highly inclined upwards; and it is remarkable that the nocturnal movemeut is almost wholly confined to the blades, being effected by the pulvinus at their bases; whilst the petioles retain day and night nearly the same inclination. On this night (Nov. 23rd), and for some few succeeding nights, the blades rose from a horizontal into a vertical position, and then became bowed inwards at about an average angle of 10°; so that they had passed through an angle of 100°. Their tips now almost touched one another, their bases being slightly divergent. The two blades thus formed a highly inclined roof over the axis of the seedling. This movement is the same as that of the terminal leaflet of the tripartite leaves of many species of Trifolium. After an interval of 8 days (Nov. 29th) the blades were horizontal during the day, and vertical at night, and now they were no longer bowed inwards. They continued to move in the same manner for the following two months, by which time they had increased greatly in size, their petioles being no less than °8 of an inch in length, and two true leaves had by this time been developed.

Trifolium strictum.—On the first day after germination the cotyledons, which are provided with a pulvinus, stood at noon horizontally, and at night rose to only about 45° above the horizon. Four days afterwards the seedlings were again ob- served at night, and now the blades stood vertically and were in contact, excepting the tips, which were much deflexed, so that they faced the zenith At this age the petioles are curved upwards, and at night, when the bases of the blades are in con- tact, the two petioles together form a vertical ring surrounding the plumule. The cotyledons continued to act in nearly the same manner for 8 or 10 days from the period of germination; but the petioles had by this time become straight and had increased much in length. After from 12 to 14 days the first simple true leaf was formed, and during the ensuing fortnight a remarkable movement was repeatedly observed. At I. (Fig. 125) we have a sketch, made in the middle of the day, of a seedling about a fortnight old. The two cotyledons, of which &e is the light, and Le the left one, stand directly opposite one another,

Trifolium strictum; diurnal and nocturnal positions of the two cotyledons and of the first leaf. I. Seedling viewed obliquely from above, during the day: Re, right cotyledon; Zc, left cotyledon; F, first true leaf. II. A rather younger seedling, viewed at night: 2c, right cotyledon raised, but its position not otherwise changed ; Le, left cotyledon rai-ed and laterally twisted; J, first leaf raised and twisted so as to face the lett twisted cotyledon. IL. Same seedling viewed at night from the opposite side. The back of the first leaf, F, is here shown instead of the front, as in IL

and the first true leaf (2) projects at right angles to them. At night (see IL and III.) the right cotyledon (Rc) is greatly raised, but is not otherwise changed in position. The left cotyledon (Zc) is likewise raised, but it is also twisted, so that its blade, instead of exactly facing the opposite one, now stands at nearly right angles to it This nocturnal twisting movement is effected not by means of the pulvinus, but by the twisting of the whole length of the petiole, as could be seen by the curved jine of its upper concave surface. At the same time the true leaf (/’) rises up, so as to stand vertically, or it even passes the vertical and is inclined a little inwards. It also twists a little, by which means the upper surface of its blade fronts, and almost comes into contact with, the upper surface of the twisted