{Semicircle, from the light in 2nd circle was made in 2 hrs. 47 m. { 1 hr. 17 m., to the light 1 hr.
{ 30 m.: difference 13 m.
Ipomaea jucunda (Convolvulaceae) moves against the sun, placed in my study, with windows facing the north-east. Weather hot.
{Semicircle, from the light in 1st circle was made in 5 hrs. 30 m. { 4 hrs. 30 m., to the light 1 hr.
{ 0 m.: difference 3 hrs. 30 m.
2nd circle was made in 5 hrs. {Semicircle, from the light in 20 m. (Late in afternoon: { 3 hrs. 50 m., to the light 1 hr.
circle completed at 6 hrs. 40 m. { 30 m.: difference 2 hrs. 20 m.
P.M.)
We have here a remarkable instance of the power of light in r.e.t.a.r.ding and hastening the revolving movement. (See ERRATA.)
Convolvulus sepium (large-flowered cultivated var.) moves against the sun. Two circles, were made each in 1 hr. 42 m.: difference in semicircle from and to the light 14 m.
Rivea tiliaefolia (Convolvulaceae) moves against the sun, made four revolutions in 9 hrs.; so that, on an average, each was performed in 2 hrs. 15 m.
Plumbago rosea (Plumbaginaceae) follows the sun. The shoot did not begin to revolve until nearly a yard in height; it then made a fine circle in 10 hrs. 45 m. During the next few days it continued to move, but irregularly. On August 15th the shoot followed, during a period of 10 hrs. 40 m., a long and deeply zigzag course and then made a broad ellipse. The figure apparently represented three ellipses, each of which averaged 3 hrs. 38 m. for its completion.
Jasminum pauciflorum, Bentham (Jasminaceae), moves against the sun.
A circle was made in 7 hrs. 15 m., and a second rather more quickly.
Clerodendrum Thomsonii (Verbenaceae) follows the sun.
H. M.
April 12, 1st circle was made in 5 45 (shoot very young) 14, 2nd 3 30 {(directly after the 18, a semicircle 5 0 { plant was shaken { on being moved) 19, 3rd circle 3 0 20, 4th 4 20
Tecoma jasminoides (Bignoniaceae) moves against the sun.
H. M.
March 17, 1st circle was made in 6 30 19, 2nd 7 0 22, 3rd 8 30 (very cold day) 24, 4th 6 45
Thunbergia alata (Acanthaceae) moves against sun.
H. M.
April 14, 1st circle was made in 3 20 18, 2nd 2 50 18, 3rd 2 55 18, 4th 3 55 (late in afternoon)
Adhadota cydonaefolia (Acanthaceae) follows the sun. A young shoot made a semicircle in 24 hrs.; subsequently it made a circle in between 40 hrs. and 48 hrs. Another shoot, however, made a circle in 26 hrs. 30 m.
Mikania scandens (Compositae) moves against the sun.
H. M.
March 14, 1st circle was made in 3 10 15, 2nd 3 0 16, 3rd 3 0 17, 4th 3 33 April 7, 5th 2 50 7, 6th 2 40 {This circle was made { after a copious water- { ing with cold water at { 47 degrees Fahr.
Combretum argenteum (Combretaceae) moves against the sun. Kept in hothouse.
H. M.
{Early in morning, when Jan. 24, 1st circle was made in 2 55 { the temperature of the { house had fallen a { little.
24, 2 circles each at an } average of } 2 20 25, 4th circle was made in 2 25
Combretum purpureum revolves not quite so quickly as C. argenteum.
Loasa aurantiaca (Loasaceae). Revolutions variable in their course: a plant which moved against the sun.
H. M.
June 20, 1st circle was made in 2 37 20, 2nd 2 13 20, 3rd 4 0 21, 4th 2 35 22, 5th 3 26 23, 6th 3 5
Another plant which followed the sun in its revolutions.
H. M.
July 11, 1st circle was made in 1 51 } 11, 2nd 1 46 } Very hot day.
11, 3rd 1 41 } 11, 4th 1 48 } 12, 5th 2 35 }
Scyphanthus elegans (Loasaceae) follows the sun.
H. M.
June 13, 1st circle was made in 1 45 13, 2nd 1 17 14, 3rd 1 36 14, 4th 1 59 14, 5th 2 3
Siphomeris or Lecontea (unnamed sp.) (Cinchonaceae) follows the sun.
H. M.
{(shoot extremely May 25, semicircle was made in 10 27 { young) 26, 1st circle 10 15 (shoot still young) 30, 2nd 8 55 June 2, 3rd 8 11 6, 4th 6 8 { Taken from the 8, 5th 7 20 { hothouse, and 9, 6th 8 36 { placed in a room { in my house.
Manettia bicolor (Cinchonaceae), young plant, follows the sun.
H. M.
July 7, 1st circle was made in 6 18 8, 2nd 6 53 9, 3rd 6 30
Lonicera brachypoda (Caprifoliaceae) follows the sun, kept in a warm room in the house.
H. M.
April, 1st circle was made in 9 10 (about) {(a distinct shoot, very April, 2nd circle was made in 12 20 { young, on same plant) 3rd 7 30 {In this latter circle, { the semicircle from { the light took 5 hrs.
4th 8 0 { 23 m., and to the { light 2 hrs. 37 min.: { difference 2 hrs 46m.
Aristolochia gigas (Aristolochiaceae) moves against the sun.
H. M.
July 22, 1st circle was made in 8 0 (rather young shoot) 23, 2nd 7 15 24, 3rd 5 0 (about)
In the foregoing Table, which includes twining plants belonging to widely different orders, we see that the rate at which growth travels or circulates round the axis (on which the revolving movement depends), differs much. As long as a plant remains under the same conditions, the rate is often remarkably uniform, as with the Hop, Mikania, Phaseolus, &c. The Scyphanthus made one revolution in 1 hr.
17 m., and this is the quickest rate observed by me; but we shall hereafter see a tendril-bearing Pa.s.siflora revolving more rapidly. A shoot of the Akebia quinata made a revolution in 1 hr. 30 m., and three revolutions at the average rate of 1 hr. 38 m.; a Convolvulus made two revolutions at the average of 1 hr. 42 m., and Phaseolus vulgaris three at the average of 1 hr. 57 m. On the other hand, some plants take 24 hrs. for a single revolution, and the Adhadota sometimes required 48 hrs.; yet this latter plant is an efficient twiner. Species of the same genus move at different rates. The rate does not seem governed by the thickness of the shoots: those of the Sollya are as thin and flexible as string, but move more slowly than the thick and fleshy shoots of the Ruscus, which seem little fitted for movement of any kind. The shoots of the Wistaria, which become woody, move faster than those of the herbaceous Ipomoea or Thunbergia.
We know that the internodes, whilst still very young, do not acquire their proper rate of movement; hence the several shoots on the same plant may sometimes be seen revolving at different rates. The two or three, or even more, internodes which are first formed above the cotyledons, or above the root-stock of a perennial plant, do not move; they can support themselves, and nothing superfluous is granted.
A greater number of twiners revolve in a course opposed to that of the sun, or to the hands of a watch, than in the reversed course, and, consequently, the majority, as is well known, ascend their supports from left to right. Occasionally, though rarely, plants of the same order twine in opposite directions, of which Mohl (p. 125) gives a case in the Leguminosae, and we have in the table another in the Acanthaceae. I have seen no instance of two species of the same genus twining in opposite directions, and such cases must be rare; but Fritz Muller {16} states that although Mikania scandens twines, as I have described, from left to right, another species in South Brazil twines in an opposite direction. It would have been an anomalous circ.u.mstance if no such cases had occurred, for different individuals of the same species, namely, of Solanum dulcamara (Dutrochet, tom. xix. p. 299), revolve and twine in two directions: this plant, however; is a most feeble twiner. Loasa aurantiaca (Leon, p. 351) offers a much more curious case: I raised seventeen plants: of these eight revolved in opposition to the sun and ascended from left to right; five followed the sun and ascended from right to left; and four revolved and twined first in one direction, and then reversed their course, {17} the petioles of the opposite leaves affording a point d"appui for the reversal of the spire. One of these four plants made seven spiral turns from right to left, and five turns from left to right. Another plant in the same family, the Scyphanthus elegans, habitually twines in this same manner. I raised many plants of it, and the stems of all took one turn, or occasionally two or even three turns in one direction, and then, ascending for a short s.p.a.ce straight, reversed their course and took one or two turns in an opposite direction. The reversal of the curvature occurred at any point in the stem, even in the middle of an internode. Had I not seen this case, I should have thought its occurrence most improbable. It would be hardly possible with any plant which ascended above a few feet in height, or which lived in an exposed situation; for the stem could be pulled away easily from its support, with but little unwinding; nor could it have adhered at all, had not the internodes soon become moderately rigid. With leaf- climbers, as we shall soon see, a.n.a.logous cases frequently occur; but these present no difficulty, as the stem is secured by the clasping petioles.
In the many other revolving and twining plants observed by me, I never but twice saw the movement reversed; once, and only for a short s.p.a.ce, in Ipomoea jucunda; but frequently with Hibbertia dentata.