The Power of Movement in Plants

Solanum palinacanthum: circumnutation of an arched hypocotyl, just emerging from the ground, with the two legs tied together, traced in darkness on a horizontal glass, from 9.20 a.m. Dec. 17th to 8.30 A.M. 19th. Movement of bead magnified 13 times; but the filament, which was affixed obliquely to the crown of the arch, was of unusual length. summit of which was on a level with the surface of the soil, were tied together; the earth having been previously removed to a little depth all round. The movement of the arch during 47. hours under these unnatural circumstances is exhibited in the annexed figure.

The cotyledons of some seedlings in the hot-house were hori- zontal about noon on December 13th; and at 10 p.m. had risen to an angle of 27° above the horizon; at 7 a.m. on the following 52 Cuay. Y morning, before it was light, they had risen to 59° above the horizon; in the afternoon of the same day they were found again horizontal. : Beta vulyaris (Chenopodez).—The seedlings are excessively sensitive to light, so that although on the first day they were uncovered only during two or three minutes at each observation, they all moved steadily towards the side of the room whence the light proceeded, and the trac- ings consisted only of slightly zigzag lines directed towards the light. On the next day the plants were placed in a completely darkened room, and at each observation were iluminated as much as possible from vertically above by a small wax taper. The annexed figure (Fig. 39) shows the move- ment of the hypocotyl during 9 h. under these circumstances. A second seedling was similarly observed at the same time,

nutation of hypo- cotyl, with filament fixed obliquely a- cross its summit, traced in darkness on horizontal ‘glass, from 8.25 A.M. to 5.30 p.m. Nov. 4th. Movement of bead magnified 23 times, here reduced to one- third of original scale. and the tracing had the same peculiar character, due to the hypocotyl often mov- ing and returning in nearly parallel lines. The movement of a third hypocotyl differed greatly. We endeavoured to trace the movements of the cotyledons, and for this purpose some seedlings were kept in the dark, but they moved in an abnormal manner; they continued rising from 8.45 a.m. to 2 P.m.,

then moved laterally, and from 8 to 6 P.M. descended; whereas cotyledons which have been exposed all the day to the light rise in the evening so as to stand verti- cally at night; but this statement applies only to young seedlings. For instance, six seedlings in the greenhouse had their cotyledons partially open for the first time on the morning of November 15th, and at 8.45 p.m. all were completely closed, 80 that they might properly be said to be asleep. Again, on the morning of November 27th, the cotyledons of four other seedlings, which were surrounded by a collar of brown paper so that they received light only from above, were open to the extent of 39°; at 10 p.m. they were completely closed; next morning (November 28th) at 6.45 a.m., whilst ‘t was still dark, two of them

were partially open and all opened in the course of the morning; but at 10.20 p.m. all four (not to mention nine others which had been open in the morning and six others on another ocea- sion) were again completely closed. On the morning of the 29th they were open, but at night only one of the four was closed, and this only partially; the three others had their cotyledons much more raised than during the day. On the night of the 30th the cotyledons of the four were only slightly raised,

Ricinus Borboniensis (Euphorbiacez).— Seeds were purchased under the above naine—probably a variety of the common castor- oil plant. As soon as an arched hypocotyl had risen clear above the ground, a filament was attached to the upper leg bearing the cotyledons which were still buried beneath the surface, and the movement of the bead was traced on a horizontal glass during a period of 84h. The lines traced were strongly zigzag, and as the bead twice returned nearly parallel to its former course in two different directions, there could be no doubt that the arched hypocotyl circumnutated. At the close of the 34 h. the upper part began to rise and straighten itself, dragging the cotyledons out of the ground, so that the movements of the bead could no longer be traced on the glass.

Quercus (American sp.) (Oupuliferee).—Acorns of an American oak which had germinated at Kew were planted in a pot in the greenhouse. This transplantation checked their growth; but after a time one grew to a height of five inches, measured to the tips of the small partially unfolded leaves on the summit, and now looked vigorous. It consisted of six very thin internodes of unequal lengths. Considering these circumstances and the nature of the plant, we hardly expected that it would circumnutate; but the annexed figure (Fig. 40) shows that it did so im a conspicuous manner, changing its course many times and travelling in all directions during the 48 h. of observation. The figure seems to represent 5 or 6 irregular ovals or ellipses. The actual amount of movement from side to side (excluding one great bend to the left) was about ‘2 of an inch; but this was difficult to estimate, as owing to the rapid growth of the stem, the attached filament was much further from the mark beneath at the close than at the commencement of the observations. It deserves notice that the pot was placed in a north-east room within a deep box, the top of which was not at first covered up, so that the inside facing

the windows was a little more illuminated than the opposite side; and during the first morning the stem travelled to a greater distance in this direction (to the left in the figure) than it did afterwards when the box was completely protected from light Quercus (American sp.): circumnutation of young stem, traced on hori- zontal glass, from 12.50 p.m. Feb. 22nd to 12.50 p.at. 24th. Movement of bead greatly magnified at first, but slightly towards the close of the observations—about 10 times on an average.

Quercus robur.—Observations were made only on the move- ments of the radicles from germinating acorns, which were allowed to grow downwards in the manner previously described, over plates of smoked glass, inclined at angles between 65° and 69° tothe horizon. In four cases the tracks left were almost straight, but the tips had pressed sometimes with more and sometimes with less force on the glass, as shown by the varying thickness of the tracks and by little bridges of soot left across them. In the fifth case the track was slightly serpentine, that is, the tip had moved a little from side to side. In the sixth case (Fig. 41, A) it was plainly serpentine, and the tip had pressed almost equably on the glass in its whole course. In the seventh case (B) the tip had moved both laterally and had pressed

alternately with unequal force on the glass; so that it had moved a little in two planes at right angles to one another. In the eighth and last case (C) it had moved very little laterally, but had alternately left the glass and come into contact with it again. There can be no doubt that in the last four cases the 1adicle of the oak cireumnutated whilst growing downwards Quercus robur: tracks left on inclined smoked glass-plates by tips of radicles in growing downwards. Plates A and C inclined at 65° and plate B at 68° to the horizon.

Corylus avellana (Corylacese).—The epicotyl breaks through the ground in an arched form; but in the specimen which was first examined, the apex had become decayed, and the epicotyl grew to some distance through the soil, in a tortuous, almost horizontal direction, like a root. In consequence of this injury it had emitted near the hypogean cotyledons two secondary shoots, and it was remarkable that both of these were arched, like the normal epicotyl in ordinary cases. The soil was removed from around one of these arched secondary shoots, and a glass filament was affixed to the basal leg. The whole was kept damp beneath a metal-box with a glass lid, and was thus illumi- nated only from above. Owing apparently to the lateral pressure of the earth being removed, the terminal and bowed-down part of the shoot began at once to move upwards, so that after 24h. it formed a right angle with the lower part. This lower part, to which the filament was attached, also straightened itself, and moved a little backwards from the upper part. Con- sequently a long line was traced on the horizontal glass; and

On the following day the other secondary shoot was observed; it was a little more advanced in age, for the upper part, instead Corylus avellana: circumnuta- tion of a young shoot emitted from the epicotyl, the apex of which had been injured, traced on a horizontal glass, from 9 A.M. Feb. 2nd to 8 AM. 4th. Movement ot bead magnified about 27 of depending vertically downwards, stood at an angle of 45° above the horizon. The tip of the shoot pro- jected obliquely *4 of an inch above the ground, but by the close of our observations, which lasted 47 h., it had grown, chiefly towards its base, to a height of -85 of aninch. The filament was fixed transversely to the basal and almost upright half of the shoot, close beneath the lowest scale-like appendage. The circum- nutating course pursued is shown in the accompanying figure (Fig. 42). The actual distance traversed from side to side was about °04 of an inch.

Pinus pinaster (Conifers). — A young hypocotyl, with the tips of the cotyledons still enclosed within the seed-coats, was at first only *85 of an inch in height; but the upper part grew so rapidly that at the end of our observations it was -6 in height, Pinus pinaster > circumnutation of hypocotyl, with filament fixed across its summit, traced on horizontal glass, from 10 a.M. March 21st to 9 a.bl. 23rd. Seedling kept in darkness. Movement of bead magnified abcu*

and by this time the filament was attached some way down the little stem. From some unknown cause, the hypocotyl moved far towards the left, but there could be no doubt (Fig. 43) that it circumnutated. Another hypocotyl was similarly observed, and it likewise moved in a strongly zigzag lint to the same side, This lateral movement was not caused by the attachment of the glass filaments, nor by the action of light; for no light was allowed to enter when each observation was made, except from vertically above.

The hypocotyl of a seedling was secured to a little stick; it bore nine in appearance distinct cotyledons, arranged in a circle. The movements of two nearly opposite ones were observed. The tip of one was painted white, with a mark placed below, and the figure described (Fig. 44, A) shows that it made an irregular Pinus pinaster: circumnutation of two opposite cotyledons, traced on horizontal glass in darkness, from 8.45 AM. to 8.35 p.m. Nov. 25th. Movement of tip in A magnified about 22 times, here reduced to one- half of original scale. .

circle in the course of about 8 h. During the night it travelled to a considerable distance in the direction indicated by the broken line. A glass filament was attached longitu- dinally to the other cotyledon, and this nearly completed (Fig. 44, B) an irregular circular figure in about 12 hours. During the night it also moved to a considerable distance, in the direction indicated by the broken line. The cotyledons therefore circumnutate independently of the movement of the hypocotyl. Although they moved much during the night, they did not approach each other so as to stand more vertically than during the day.

Cycas-pectinata (Cycades).—The large seeds of this plant in germinating first protrude a single leaf, which breaks through the ground with the petiole bowed into an arch and with the leaflets involuted. A leaf in this condition, which at the close of our observations was 2} inches in height, had its movements traced in a warm greenhouse by means of a glass filament bearing paper triangles attached across its tip. The tracing (Fig. 45) s:.ows how large, complex, and rapid were the circum-

Oyeas pectinata : circumnutation of young leaf whilst emerging from the ground, feebly illuminated from above, traced on vertical glass, from 5 p.m. May 28th to 11 a.m. 31st. Movement magnified 7 times, here reduced to two-thirds of original scale. nutating movements. The extreme distance from side to side which it passed over amounted to between *6 and ‘7 of an inch, Cana Warscewiczit (Cannaces).—A seedling with the plu- mule projecting one inch above the ground was observed, but not under fair conditions, as it was brought out of the hot- house and kept in a room not sufficiently warm. Nevertheless the tracing (Fig. 46) shows that it made two or three incom- plete irregular circles or ellipses in the course of 48 hours. The plumule is straight; and this was the first instance observed

by us of the part that first breaks through the ground uot heing arched. Canna Warscewiczii: circumnutation of plumule with filament affixed obliquely to outer sheath-like leaf, traced in darkness onhorizontal glass from 8.45 a.m. Noy. 9th to 8.10 A.a1, 11th. Movement of bead mag- nified 6 times. Allium cepa (Liliacee).—The narrow green leaf, which pro- trudes from the seed of the common onion as a cotyledon,* breaks through the ground in the form of an arch, in the same manner as the hypocotyl or epicotyl of a dicotyledonous plant. Long after the arch has risen above the surface the apex remains within the seed-coats, evidently absorbing the still abundant contents. The summit or crown of the arch, when it first protrudes from the seed and is still buried beneath the ground, is simply rounded; but before it reaches the surface it is developed into a conical protuberance of a white colour (owing to the absence of chlorophyll), whilst the adjoining parts are green), with the epidermis apparently rather thicker and tougher than elsewhere. We may therefore conclude that this conical protuberance is a special adaptation for breaking through the ground,t and answers the same end as the knife-like white crest on the summit of the straight cotyledon of the Graminez.

= This is the expression used purpose which it subserves. He t+ Haberlandt has briefiy de- scribed (‘Die Schutzcinrichtun- gen... Keimpflanze,’ 1877, p. 77) this curious structure and the states that good figures of the cotyledon of the onion liave been given by Tiltmann and by Sacia in his ‘Experimental Physiologie,’ p. 93. and rises up, forming a right angle, or more commonly a still larger angle with the lower part, and occasionally the whole originally formed the crown of the arch, is now seated on one

side, and appears like a joint or knee, which from acquiring chlorophyll becomes green, and increases in size. In rarely or never becoming perfectly straight, these cotyledons differ remark- ably from the ultimate condition of the arched hypocotyls or epicotyls of dicotyledons. It is, also, a singular circumstance Allium cepu: circunnu- figure described resembled pretty closely tation of basal half that above given; and this shows that the of arched cotyledon A $i

traced in darkness on Chief seat of movement is in the lower or horizontal glass, from basal part of the cotyledon. beneath the surface, and the earth was then removed all round tothe depth of 3 inch. A glass filament was affixed obliquely to it, and the movement of the bead, magnified 17 times, was traced the right,and during the next two hours it returned in a roughly parallel but strongly zigzag course. From some unknown cause it had grown up through the soil in an inclined direction, and

the same general direction, but in a slightly zigzag manner, until it became upright. On the following morning it changed its course completely. There can therefore hardly be a doubt that the plumule circumnutates, whilst buried beneath the ground, as much as the pressure of the surrounding earth will permit. The surface of the soil in the pot was now covered with a thin layer of very fine argillaceous sand, which was kept damp; and after. the tapering seedlings had grown a few tenths of an inch in height, each was found surrounded by a little open space or circular crack; and this could be accounted for only by their having circumnutated and thus pushed away the sand on all sides; for there was no vestige of a crack in any other part.

Asparagus officinalis : circumnutation of plumules with tips whitened and marks placed beneath, traced on a norizontal glass. A, young plumule; movement traced from 8.30 a.m. Nov. 30th to 7.15 A.M. next morning ; magnitied about 35 times. B, older plumule; movement traced from 10.15 A.M, to 8.10 P.M. Nov. 29tii; magnified 9 times, but here reduced to one-half of original scale. ments of five seedlings, varying in height from ‘3 inch to 2 inches, were traced. They were placed within a box and illuminated from above; but in all five cases the longer axes of the figures described were directed to nearly the same point; so that more light seemed to have come through the glass roof of the green- house on one side than on any other. All five tracings re- sembled each other to a certain extent, and it will suffice to give two of them. In A (Fig. 48) the seedling was only -45 of an

inch in height, and consisted of a single internode bearing a bud on its summit. he apex described between 8.30 a.m. and 10.20 pm. (ie. during nearly 14 hours) a figure which would probably have consisted of 33 ellipses, had not the stem been drawn to one side until Lv.m., after which hour it moved back- wards. On the following morning it was not far distant from the point whence it had first started. The actual amount of movement of the apex from side to side was very small, viz. about jth of an inch. The seedling of which the movements are shown in Fig. 48, B, was 1} inch in height, and consisted of three internodes besides the bud on the summit. The figure, which was described during 10h., apparently represents two irregular and unequal ellipses or circles. The actual amount of movement of the apex, in the line not influenced by the light, was *11 of an inch, and in that thus influenced °37 of an inch. With a seedling 2 inches in height it was obvious, even without the aid of any tracing, that the uppermost part of the stem bent snecessively to all points of the compass, like the stem of a twining plant. A little increase in the power of circumnutating and in the flexibility of the stem, would convert the common asparagus into a twining plant, as has occurred with one species in this genus, namely, A. scandens,

Phalaris Canariensis (Graminew).— With the Gramines the part which first rises above the ground has been called by some authors the pileole; and various views have been expressed on its homological nature. It is considered by some great authori- ties to be a cotyledon, which term we will use without venturing to express any opinion on the subject.* It consists in the present case of a slightly flattened reddish sheath, terminating upwards in a sharp white edge; it encloses a true green leaf, which protrudes from the sheath through a slit-like orifice, close beneath and at right angles to the sharp edge on the summit. The sheath is not arched when it breaks through the ground,

The movements of three rather old seedlings, about 1} inch in height, shortly before the protrusion of the leaves, were first traced. They were illuminated exclusively from above; for, as will hereafter be shown, they axe excessively sensitive to tha * We are indebted to the Rey, — this subject, together with re G. Henslow for an abstract of the ferences, views which have becn held on action of light; and if any enters even temporarily on one side, they merely bend to this side in slightly zigzag lines. Of the three tracings one alone (Fig. 49) is here given. Had the observations

been more frequent during the 12h. two oval figures would have been described with their longer axes at right angles to one another. The actual amount of movement of the apex from side to side was about ‘dof an inch. The figures described by the other two seedlings resembled to a certain extent the one here given. A seedling which had just broken through the ground and projected only th of an inch above the surface, was next observed in the same manner as before. It was necessary to clear away the earth all round the seedling to a little depth in order to place a mark beneath the apex.

Phaluris Conariensis: cireumnu- tation of a cotyledon, with a mark placed below the apex, traced on a horizontal glass, from 8.35 a.m. Nov. 26th to 8.45 4.M. 27th. Movement of apex magnified 7 times, here reduced to one-half scale. course of the ten hours of observa- tion ; so that there can be no doubt about its circumnutation. The cause of the general movement in one direction could hardly be attributed to the entrance of lateral light, as this was carefully guarded against; and we suppose it was in some manner connected with the removal of the earth round the little seedling.

Lastly, the soil in the same pot was searched with the aid of a lens, and the white knife-like apex ofa seedling was found on an exact level with that of the surrounding surface. Phalaris Canariensis : cireumnu- tation of a very young coty- ledon, with a mark placed below the apex, traced on a horizontal glass, from 11,37 AM. to 9.30 p.M. Dec. 15th. Movement of apex greatly magnified, here reduced to one-forrth of original scale. of a quarter of an inch, the seed itself remaining covered. The pot, protected from lateral light, was placed under the micro-