The Power of Movement in Plants

7 s Verbena melindres: circumnutation of stem in darkness, traced on vertical upright to the tip, and its movements were traced during 41 h. 30 m. on a vertical glass (Fig. 82). Under these circum- stances the lateral movements were chiefly shown; but as the lines from side to side are not on the same level, the shoot must have moved in a plane at right angles to that of the lateral movement, that is, it must have cireumnutated. On the next day (6th) the shoot moved in the course of 16 h. four times to the right, and four times to the left; and this apparently represents the formation of four ellipses, so that each was completed in 4 h.

(17.) Ceratophyllum demersum (Ceratophy lec, Fam. 220).—An interesting account of the movements of the stem of this water- plant has been published by M. E. Rodier.* The movements are confined to the young internodes, becoming less and less lower down the stem; and they are extraordinary from their amplitude. The stems sometimes moved through an angle of above 20° in 6 h., and in one instance through 220° in 3h. They generally bent from right to left in the morning, and in an opposite direc- tion in the afternoon ; but the movement was sometimes tempo- rarily reversed or quite arrested. It was not affected by light. It does not appear that M. Rodier made any diagram on a hori- zontal plane represeriting the actual course pursued by the apex, but he speaks of the “branches executing round their axes of growth a.movement of torsion.” From the particulars above given, and remembering in the case of twining plants and of tendrils, how difficult it is not to mistake their bending to all points of the compass for true torsion, we are led to believe that the stems of this Ceratophyllum circumnutate, probably in the shape of narrow ellipses, each completed in about 26 h. The following statement, however, seems to indicate something different from’ ordinary circumnutation, but we cannot fully understand it. M. Rodier says: “Il est alors facile de voir que le mouvement de flexion se produit d’abord dans les mérithalles supérieurs, qu’il se propage ensuite, en s’amoindrissant du huut en bas; tandis qu'au contraire le mouvement de redressement commence par la partie inférieure pour se terminer & la partie supérieure qui, quelquefois, peu de temps avant de se relever tout & fait, forme avec l’axe un angle trés aigu.” :

(18) Coniferce—Dr. Maxwell Masters states (‘ Journal Linn Soe.,’ Dec. 2nd, 1879) that the leading shoots of many Conifers during the season of their active growth exhibit very remark- able movements of revolving nutation, that is, they circumnu- tate. We may feel sure that the lateral shoots whilst growing would exhibit the same movement if carefully observed. Lilium aurctun: cireumnutation of a stem in darkness, traced on a horizontal glass, from 8 A.M. on March 14th to 8.35 a.m. on 16th. But it should be noted that our observations were interrupted between 6 P.M. on the 14th and 12.15 p.m. on 15th, and the movements during this interval of 18h. 15m. are representel by a long broken line. Diagram reduced to half original scale.

of the stem of a plant 2! inches in height is represented in the above figure (Fig. 3). Cyperus alternifolins : cireumnutation of stem, illummated from above. traced on horizontal glass, from 9.45 a.m. March 9th to 9 P.M. on 10th The stem grew so rapidly whilst being observed, that it was not possible to estimate how much its movements were magnified in the tracing. filament, with a bead at the end, was fixed across the summit of a young stem 10 inches in height, close beneath the crown of elongated leaves. On March 8th, between 12.20 and 7.20 p.m., the stem described an ellipse, open at one end. On the follow- ing day a new tracing was begun (Fig. 84), which plainly shows that the stem completed three irregular figures in the course of 35 bh. 15 m.

Concluding Remarks on the Circumnutation of Stems.— Any one who will inspect the diagrams now given, and will bear in mind the widely separated position of the plants described in the series, —remembering that we have good grounds for the belief that the hypocotyls and epicotyls of all seedlings circumnutate,—not forgetting the number of plants distributed in the most distinct families which climb by a similar move- ment,—will probably admit that the growing stems of all plants, if carefully observed, would be found to circumnutate toa greater or less extent. When we treat of the sleep and other movements of plants, many other cases of circumnutating stems will be incidentally given. In looking at the diagrams, we should remember that the stems were always growing, so that in each case the circumnutating apex as it rose will have described a spire of some kind. The dots were made on the glasses generally at intervals of an hour, or hour and a half, and were then joined by straight lines. If they had been made at intervals of 2 or 8 minutes, the lines would have been more curvilinear, as in the case of the tracks left on the smoked glass-plates by the tips of the circumnutating radicles of seedling plants. The diagrams generally approach in form to a succession of more or less irregular ellipses or ovals, with their longer axes directed to different points of the compass during the same day or on succeeding days. The stems there-

fore, sooner or later, bend to all sides; but after a stem has bent in any one direction, it commonly bends back at first in nearly, though not quite, the opposite direction; and this gives the tendency to the formation of ellipses, which are generally narrow, but not so narrow as those described by stolons and leaves. On the other hand, the figures sometimes approach in shape to circles. Whatever the figure may be, the course pursued is often interrupted by zigzugs, small triangles, loops, or ellipses. A stem may describe a single large ellipse one day, and two on the next. With different plants the com- plexity, rate, and amount of movement differs much. ‘The stems, for instance, of Iberis and Azalea deseribed only a single large ellipse in 24 h.; whereas those of the Deutzia made four or five deep zigzags or narrow ellipses in 11} h., and those of the Trifolium three triangular or quadrilateral figures in 7h.

Stolons consist of much elongated, flexible branches, which run along the surface of the ground and form roots at a distance from the parent-plant. They are therefore of the same homological nature as stems; and the three following cases may be added to the twenty previously given cases. Frayariu (cultivated garden var.): Losacce.—A plant growing m a pot had emitted a long stolon; this was supported by a stick, so that it projected for the length of several inches hori- zontally. A glass filament bearing two minute triangles of paper was affixed to the terminal bud, which was a little up- turned ; and its movements were traced during 21 h., as shown in Fig. 85. In the course of the first 12h. it moved twice up and twice down in somewhat zigzag lines, and no doubt tra- velled in the same manner during tlie night. On the following

morning after an interval of 20 h. the apex stood a little higher than it did at first, and this shows that the stolon had not been Fraga ia: arcumnutation of stolon, kept in darkness, traced on vertical glass, from 10.45 A.M. May 18th to 7.45 a.M. on 19th. acted on within this time by geotropism;* nor had its own weight caused it to bend downwards. On the following morning (19th) the glass filament was detached and refixed close behind the bud, as it appeared pos- sible that the circumnutation of the terminal bud and of the adjoining part of the stolon might be different. The movement was now traced during two consecutive days (Fig. 86). During the first day the filament travelled in the course of 14h. 30 m. five times up and four times down, besides some lateral move- ment. On the 20th the course was even more complicated, and can hardly be followed in the figure; but the filament moved in 16h. at least five times up and five times down, with very little

* Dr. A. B. Frank states (‘Die acted on by geotropism, but only Naturliche wagerechte Richtungz after a considerable interval of von Pflanzentheilen,’ 1870, p.20) time. that the stolons of this plant ure lateral deflection. The first and last dots made on this second day, viz., at 7 a.m. and 11 p.m., were close together, showing that the stolon had not fallen or risen. Nevertheless, by com- paring its position on Fig. 86. the morning of the 19th and 21st, it is obvious that the stolon had sunk; and this may be attri- buted to slow bending So..m.19" down either from its own weight or from geotro-

During a part of the 20th an orthogonal tracing was made by applying a cube Beem of wood to the vertical Se glass and bringing the apex of the stolon at suc- \. cessive periods into a line with one edge; a dot being made each time on the glass. This tracing therefore represented very nearly the actual amount of movement of the apex; and in the course of 9 h. the distance of the ex- y treme dots from one an- i other was ‘45 inch. By the same method it was ascertained that the apex ' moved between 7 A.M. on Sa.m.2t" the 20th and 8 a.m. on the

Fragaria : circumnutation of the same stolon 21sta distance of ‘82 inch. as in the last figure, observed in the same manner, and traced from 8 A.M. May 19th A younger and shorter to 8 A.M. 2ist. stolon was supported so that it projected at about 45° above the horizon, and its movement was traced by the same orthogonal method. On the first day the apex soon rose above the field of vision. By the next morning it had sunk, and the course pursued was now traced during 14 h. 30 m. (Fig. 87). The amount of movement was almost the same,

from side to side as up and down; and differed in this respect remarkably from the movement in the previous cases.’ During the latter part of the day, viz., between 3 and 10.30 p.m., tho Fragavia: cireumnutation of another and younger stolon, traced from 8 a.br. to 10.30 p.m. Figure reduced to one-half of original scale. actual distance travelled by the apex amounted to 115 inch; and in the course of the whole day to at least 2°67 inch. This is an amount of movement almost comparable with that of some climbing plants. The same stolon was observed on the following day, and now it moved in a somewhat less complex manner, in a plane not far from vertical, The extreme amount of actual movement was 1°55 inch in one direction, and ‘6 inch in another direction at right angles. During neither of these days did the stolon bend downwards through geotropism or its own weight.

Four stolons still attached to the plant were laid on damp sand in the back of a room, with their tips facing the north-east windows. They were thus placed because De Vries says * that they are apheliotropic when exposed to the light of the sun; but we could not perceive any effect from the above feeble degree of illumination. We may add that on another occasion, late in the sumer, some stolons, placed upright before a south-west window an a cloudy day, became distinctly curved towards the light, and were therefore heliotropic. Close in front of the tips of the prostrate stolons, a crowd of very thin sticks and the dried haulms of grasses were driven into the sand, to represent the crowded stems of surrounding plants in a state of nature. This was done for the sake of observing how the growing stolons would pass through them. They did so easily in the course of 6 days, and their circumnutation apparently facilitated their passage. When the tips encountered sticks so close together that they could not pass between them, they rose up and passed over them. ‘The sticks and haulms were removed after the passage of the four stolons, two of which were found to have assumed a permanently sinuous shape, and two were still straight. But to this subject we shall recur under Saxifraga. Saxifraga sarmentosa (Saxifragee).—A plant in a suspended pot had emitted long branched stolons, which depended like

Saxifraga sarmentosa: circumnutation of an inclined stolon, traced in darkness on a horizontal glass, from 7.45 a.m. April 18th to 9 a.m, on 9th. Movement of end of stolon magnified 2-2 times. threads on all sides. Two were tied upso as to stand vertically, and their upper ends became gradually bent downwards, but so slowly in the course of several days, that the bending was pro- bably due to their weight and not to geotropism. A glass fila- ment with little triangles of paper was fixed to the end of one of these stolons, which was 17} inches in length, and had already become much bent down, but still projected at a considerable angle above the horizon. It moved only slightly three times from side to side and then upwards; on the following day

the movement was even less. As this stolon was so long we thought that its growth was nearly completed, so we tried another which was thicker and shorter, viz., 10} inches in length. It moved greatly, chiefly upwards, and changed its course five times in the course of the day. During the night it curved sc much upwards in opposition to gravity, that the movement could no longer be traced on the vertical glass, and a horizontal one had to be used. The movement was followed during the next 25 h., as shown in Fig. 88. Three irregular ellipses, with their longer axes somewhat differently directed, were almost completed in the first 15h. The extreme actual amount of movement of the tip during the 25 h. was °75 inch.

Several stolons were laid on a flat surface of damp sand, in the same manner as with those of the strawberry. The friction of the sand did not interfere with their circumnutation ; nor could we detect any evidence of their being sensitive to contact. In order to see how in a state of nature they would act, when encountering a stone or other obstacle on the ground, short pieces of smoked glass, an inch in height, were stuck upright into the sand in front of two thin lateral branches. Their tips scratched the smoked surface in various directions; one made three upward and two downward lines, besides a nearly hori- zontal one; the other curled quite away from the glass; but ultimately both surmounted the glass and pursued their original course. The apex of a third thick stolon swept up the glass in a eurved line, recoiled and again came into contact with it ; it then moved to the right, and after ascending, descended vertically ; ultimately it passed round one end of the glass instead of over it.

Many long pins were next driven rather close together into the sand, so as to form a crowd in front of the same two thin lateral branches; but these easily wound their way through the crowd. <A thick stolon was much delayed in its passage ; at one place it was forced to turn at right angles to its former course; at another place it could not pass through the pins, and the hinder part became bowed; it then curved upwards and passed through an opening between the upper part of some pins which happened to diverge; it then descended and finally emerged through the crowd. This stolon was rendered perma- nently sinuous toa slight degree, and was thicker where sinuous than elsewhere, apparently from its longitudinal growth having been checked.

of damp moss had emitted 2 stolons, 22 and 20 inches in length. One of these was supported, so that a length of 44 inches pro. jected in a straight and horizontal line, and the movement of the apex was traced. The first dot was made at 9.10 a.m. Cotyledon umbilicus: circumnutation of stolon, traced from 11.15 A.M Aug. 25th to 11 a.m. 27th. Plant illuminated from above. Th* terminal internode was *25 inch in length, the penultimate 2°25, ana the third 3°0 inches in length. Apex of stolon stood at a distance of 5°75 inches from the vertical glass ; but it was not possible to ascertain how much the tracing was magnified, as it was not known how great a length of the internode circumnutated.

the terminal portion soon began to bend downwards and con- tinued to do so until noon. Therefore a straight line, very nearly as long as the whole figure here given (Fig. 89), was first traced on the glass; but the upper part of this line has not been copied in the diagram. The curvature occurred in the middle of the penultimate internode; and its chief seat was at the distance of 1+ inch from the apex; it appeared due to the weight of the terminal portion, acting on the more flexible part of the internode, and not to gcotropism. The apex after thus sinking down from 9,10 a.m. to noon, moved a little to tha left; it then rose up and circumnutated iu a nearly vertical plane until 10.85 p.m. On the following day (26th) it was ob-

ame 6°4o!um.279 Cotyledon umbilicus: circumnutation and downward movement of another Apex close to glass, so that figure but little magnified, and here reduced to two-thirds of original size. served from 6.40 a.m. to 5.20 p.m., and within this time it moved twice up and twice down. On the morning of the 27th the apex stood as high as it did at 11.30 4.m. on the 25th. Nor did it sink down during the 28th, but continued to cireumnutate about the same place.

respect, was olscrved during the same two days, but only twa inches of the terminal portion was allowed to project frecly and horizontally. On the 25th it continued from 9.10 a.m. to 1.30 r to bend straight downwards, apparently owing to its weight (Fig. 90); but after this hour until 10.35 p.m. it Zigzagecd. This fact deserves notice, for we here probably see the combined effects of the bending down from weight and of circumnutation. The stolon, however, did not circumnutate when it first began to bend down, as may be observed in the present diagram, and as was still more evident in the last case, when a longer portion of the stolon was left unsupported. On the following day (26th) the stolon moved twice up and twice down, but still con- tinued to fall; in the evening and during the night it travelled from some unknown cause in an oblique direction.

We sce from these three cases that stolons or runners circumnutate in a very complex manner. The lines generally extend in a vertical plane, and this may probably be attributed to the effect of the weight of the unsupported end of the stolon; but there is always some, and occasionally a considerable, amount of lateral movement. The circumnutation is so great in amplitude that it may almost be compared with that of climbing plants. That the stolons are thus uided in passing over obstacles and in winding between the stems of the surrounding plants, the observations above given render almost certain. If they had not circumnutated, their tips would have been liable to have been doubled up, as often as they met with obstacles in their path ; but as it is, they easily avoid them. This must be a considerable advantage to the plant in spreading from its parent-stock ; but we are far from supposing that the power has been gained by the stolons for this purpose, for circumnutation seems to be of universal occurrence with all growing parts; but it is not improbable that the amplitude of the movement may have been specially increased for this purpose.

We did not think it necessary to make any special observations on the circumnutation of flower-stems, these being axial in their nature, like stems or stolons ; but some were incidentally made whilst attending to other subjects, and these we will here briefly give. A few observations have also been made by other botanists. These taken together suffice to render it probable that all peduncles and sub-peduncles cir- cumnutate whilst growing. Oxalis carnosa.—The peduncle which springs frora the thick and woody stem of this plant bears three or four sab-peduncles.

Ozxalis carnosa: flower-stem, feebly illuminated from above, its circumnuta tion traced from 9 a.m. April 13th to 9 a.m. 15th, Summit of flower 8 inches beneath the horizontal glass. Movement probably magnified about 6 times, A filament with little triangles of paper was fixed within the calyx of a flower which stood upright. Its movements were observed for 48h.; during the first half of this time the flower was fully expanded, and during the second half withered. The figure here given (Fig. 91) represents 8 or 9 ellipses. Although the main peduncle cireumnutated, and described one large and

two smaller ellipses in the course of 21h., yet the chief seat ol movement lies in the sub-peduncles, which ultimately bend vertically downwards, as will be described in a future chapter. Tho peduncles of Owalis acetosella likewise bend downwards, and afterwards, when the pods are nearly mature, upwards; and this is effected by a circumnutating movement. It may be seen in the above figure that the flower-stem of , O.carnosa circumnutated during two days about the same spot. On the other hand, the flower-stem of U. sensitiva undergoes a strongly marked, daily, periodical change of position, when kept at a proper temperature. In the middle of the day it stands vertically up, or at a high angle; in the afternoon it sinks, and in the evening projects horizontally, or almost horizontally, rising again during the night. This movement continues from the period when the flowers are in bud to when, as we believe, the pods are mature: and it ought perhaps to have been included amongst the so-called sleep-movements of plants. A tracing was not made, but the angles were measured at successive periods during one whole day; and these showed that the movement was not continuous, but that the peduncle oscillated up and down. We may therefore conclude that it circumnutated. At the base of the peduncle there is a mass of small cells, forming a well-developed pulvinus, which is exteriorly coloured purple and hairy. In noother genus, as far as we know, is the peduncle furnished witha pulvinus. The peduncle of U. Ortegesii behaved differently from that of VU. sensitiva, for it stood at a less angle above the horizon in the middle of the day, than in the morning or evening. By 10.20 p.m. it had risen greatly. During the middle of the day it oscillated much up and down.

Trifolium sublerrancum.—A filament was fixed vertically to the uppermost part of the peduncle of a young and upright flower-head (the stem of the plant having been secured to a stick); and its movements were traced during 86 h. Within this time it described (see Fig. 92) a figure which represents four ellipses; but during the latter part of the time the peduncle began to bend downwards, aud after 10.30 p.m. on the 24th it curved so rapidly down, that by 6.45 a.m. on the 25th it stood only 19° above the horizon. It went on circumnutating in nearly the same position for two days. Even after the flower-heads have buried themselves in the ground they continue, as will hereafter be shown, to circumnutate. It will also be seen in the next chapter that the sub-peduncles of the separate flowers of

Trifolium repens circumnutate in a complicated course during eeveral days. I may add thatthe gynophore of Arachis hypogaa, Trifolium subterrancum: main flower-peduncle, illuminated from above, circumnutation traced on horizontal glass, from 8.40 a.m. July 23rd to 10.30 p.m. 24th. which looks exactly like a peduncle, circumnutates whilst growing vertically downwards, in order to bury the young pod in the ground. The movements of the flowers of Cyclamen Persicum were not observed ; but the peduncle, whilst the pod is forming, increases much in length, and bows itself down by a circumnutating movement. A young peduncle of Maurandia semperflorens, 13 inch in length, was carefully observed during a whole day, and it made 43 narrow, vertical. irregular and short ellipses, each at an average rate of about 2 h. 25 m. An adjoining peduncle described during the same time similar, though fewer, ellipses.* According to Sachs ¢ the fower-stems, whilst growing,

of many plants, for instance, those of Brassica napus, revolve or circumnutate; those of Allium porrum bend from side to side, and, if this movement had been traced on a horizontal glass, no doubt ellipses would have been formed. Fritz Miiller has described * the spontaneous revolving movements of the flower- stems of an Alisma, which he compares with those of a climbing lant. We made no observations on the movements of the different parts of flowers. Morren, however, has observed ¢ in the stamens of Sparmannia and Cereus a “ fren.issement spontané,” which, it may be suspected, is a circumnutating movement. The circumnutation .of the gynostemium of Stylidium, as de- scribed by Gad,t is highly remarkable, and apparently aids in the fertilisation of the flowers. The gynostemium, whilst spon- taneously moving, comes into contact with the viscid labellum, to which it adheres, until freed by the increasing tension of the parts or by being touched.

We have now seen that the flower-stems of plants belonging to such widely different families as the Cruciferee, Oxalide, Leguminose, Primulacez, Scro- phularinee, Alismacee, and Liliacee, circumnutate ; and that there are indications of this movement in many other families. With these facts before us, bearing also in mind that the tendrils of not a few plants consist of modified peduncles, we may admit without much doubt that all growing flower-stems circumnutate.

Several distinguished botanists, Hofmeister, Sachs, Pfeffer, De Vries, Batalin, Millardet, &c., have ob- p. 766. Linneeus and Treviranus (according to Pfeffer, ‘Die Pe- riodischen Bewegungen,’ &e., p. 162) state that the flower-stalks of many plants ovcupy different positions by night and day, and we shall s;e in the chapter on tle Sle-p of Plants that this im- ft ‘Sitzungbericht des bot. Ve- nae dur P. Brandenburg,’ xxi p. 84. served, and some of them with the greatest care, the periodical movements of leaves; but their attention has been chiefly, though not exclusively, directed to those which move largely and are commonly said to sleep at night. From considerations hereafter to be given, plants of this nature are here excluded, and will be treated of separately. As we wished to ascer- tain whether all young and growing leaves circumnu- tated, we thought that it would be sufficient if we observed between 80 and 40 genera, widely distributed throughout the vegetable series, selecting some un- usual forms and others on woody plants. All the plants were healthy and grew in pots. They were illuminated from above, but the light perhaps was not always sufficiently bright, as many of them were ob- served under a skylight of ground-glass. Except in a few specified cases, a fine glass filament with two minute triangles of paper was fixed to the leaves, and their movements were traced on a -vertical glass (when not stated to the contrary) in the manner already described. I may repeat that the broken lines represent the nocturnal course. The stem was always secured to a stick, close to the base of the leaf under observation. The ar- rangement of the species, with gurracenia purpurea: civeum- the number of the Family ap- — nutation of young pitcher,