The Power of Movement in Plants, Charles Darwin [the reading list book TXT] 📗

in a conspicuous manner. We will here give only a single instance (Fig. 73), showing the circumnutation of the stem of a large plant of a clover, Trifolium resupinatum. In the course of 7 h. the stem changed

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its course greatly eight times and completed three irregular circles or ellipses. It therefore circumnutated rapidly. Some of the lines run at right angles to one another.

 

Fig. 74. Rubus (hybrid): circumnutation of stem, traced on horizontal glass, from 4 P.M. March 14th to 8.30 A.M. 16th. Tracing much magnified, reduced to half of original size. Plant illuminated feebly from above.

 

(7.) Rubus idaeus (hybrid) (Rosaceae, Fam. 76).—As we happened to have a young plant, 11 inches in height and growing vigorously, which had been raised from a cross between the raspberry (Rubus idaeus) and a North American Rubus, it was observed in the usual manner. During the morning of March 14th the stem almost completed a circle, and then moved far to the right. At 4 P.M. it reversed its course, and now a fresh tracing was begun, which was continued during 40 � h., and is given in Fig. 74. We here have well-marked circumnutation.

 

(8.) Deutzia gracilis (Saxifrageae, Fam. 77).—A shoot on a bush about 18

inches in height was observed. The bead changed its course greatly eleven times in the course of 10 h. 30 m. (Fig. 75), and there could be no doubt about the circumnutation of the stem.

 

Fig. 75. Deutzia gracilis: circumnutation of stem, kept in darkness, traced on horizontal glass, from 8.30 A.M. to 7 P.M. March 20th. Movement of bead originally magnified about 20 times, here reduced to half scale.

 

(9.) Fuchsia (greenhouse var., with large flowers, probably a hybrid) (Onagrarieae, Fam. 100).—A young plant, 15 inches in height, was observed during nearly 48 h. The

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accompanying figure (Fig. 76) gives the necessary particulars, and shows that the stem circumnutated, though rather slowly.

 

Fig. 76. Fuchsia (garden var.): circumnutation of stem, kept in darkness, traced on horizontal glass, from 8.30 A.M. to 7 P.M. March 20th. Movement of bead originally magnified about 40 times, here reduced to half scale.

 

(10.) Cereus speciocissimus (garden var., sometimes called Phyllocactus multiflorus) (Cacteae, Fam. 109).—This plant, which was growing vigorously from having been removed a few days before from the greenhouse to the hot-house, was observed with especial interest, as it seemed so little probable that the stem would circumnutate. The branches are flat, or flabelliform; but some of them are triangular in section, with the three sides hollowed out. A branch of this latter shape, 9 inches in length and 1

� in diameter, was chosen for observation, as less likely to circumnutate than a flabelliform branch. The movement of the bead at the end of the glass filament, affixed to the summit of the branch, was traced (A, Fig.

77) from 9.23 A.M. to 4.30 P.M. on Nov. 23rd, during which time it changed its course greatly six times. On the 24th another tracing was made (see B), and the bead on this day changed its course oftener, making in 8 h. what may be considered as four ellipses, with their longer axes differently directed. The position of the stem and its commencing course on the following morning are likewise shown. There can be no doubt that this branch, though appearing quite rigid, circumnutated; but the [page 207]

extreme amount of movement during the time was very small, probably rather less than the 1/20th of an inch.

 

Fig 77. Cereus speciocissimus: circumnutation of stem, illuminated from above, traced on a horizontal glass, in A from 9 A.M. to 4.30 P.M. on Nov.

23rd; and in B from 8.30 A.M. on the 24th to 8 A.M. on the 25th. Movement of the bead in B magnified about 38 times.

 

(11.) Hedera helix (Araliaceae, Fam. 114).—The stem is known to be apheliotropic, and several seedlings growing in a pot in the greenhouse became bent in the middle of the summer at right angles from the light. On Sept. 2nd some of these stems were tied up so as to stand vertically, and were placed before a north-east window; but to our surprise they were now decidedly heliotropic, for during 4 days they curved themselves towards the light, and their course being traced on a horizontal glass, was strongly zigzag. During the 6 succeeding days they circumnutated over the same small space at a slow rate, but there could be no doubt about their circumnutation. The plants were kept exactly in the same place before the window, and after an interval of 15 days the stems were again observed during 2 days and their movements traced, and [page 208]

they were found to be still circumnutating, but on a yet smaller scale.

 

(12.) Gazania ringens (Compositae, Fam. 122).—The circumnutation of the stem of a young plant, 7 inches in height, as measured to the tip of the highest leaf, was traced during 33 h., and is shown in the accompanying figure (Fig. 78). Two

 

Fig. 78. Gazania ringens: circumnutation of stem traced from 9 A.M. March 21st to 6 P.M. on 22nd; plant kept in darkness. Movement of bead at the close of the observations magnified 34 times, here reduced to half the original scale.

 

main lines may be observed running at nearly right angles to two other main lines; but these are interrupted by small loops.

 

(13.) Azalea Indica (Ericineae, Fam. 128).—A bush 21 inches in height was selected for observation, and the circumnutation of its leading shoot was traced during 26 h. 40 m., as shown in the following figure (Fig. 79).

 

(14.) Plumbago Capensis (Plumbagineae, Fam. 134).—A small lateral branch which projected from a tall freely growing bush, at an angle of 35o above the horizon, was selected for observation. For the first 11 h. it moved to a considerable distance in a nearly straight line to one side, owing probably to its having been previously deflected by the light whilst standing in the greenhouse. At 7.20 P.M. on March 7th a fresh tracing was begun and continued for the next 43 h. 40 m. (see Fig. 80). During the first 2 h. it followed nearly the same direction as before, and then changed it a little; during the night it moved at nearly right angles to its previous course. Next

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day (8th) it zigzagged greatly, and on the 9th moved irregularly round and round a small circular space. By 3 P.M. on the 9th the figure had become so complicated that no more dots could be made; but the shoot continued during the evening of the 9th, the whole of the 10th, and the morning of the 11th to

 

Fig. 79. Azalea Indica: circumnutation of stem, illuminated from above, traced on horizontal glass, from 9.30 A.M. March 9th to 12.10 P.M. on the 10th. But on the morning of the 10th only four dots were made between 8.30

A.M. and 12.10 P.M., both hours included, so that the circumnutation is not fairly represented in this part of the diagram. Movement of the bead here magnified about 30 times.

 

Fig. 80. Plumbago Capensis: circumnutation of tip of a lateral branch, traced on horizontal glass, from 7.20 P.M. on March 7th to 3 P.M. on the 9th. Movement of bead magnified 13 times. Plant feebly illuminated from above.

 

circumnutate over the same small space, which was only about the 1/26th of an inch (.97 mm.) in diameter. Although this branch circumnutated to a very small extent, yet it changed its course frequently. The movements ought to have been more magnified.

 

(15.) Aloysia citriodora (Verbenaceae, Fam. 173).—The following figure (Fig. 81) gives the movements of a shoot during [page 210]

31 h. 40 m., and shows that it circumnutated. The bush was 15 inches in height.

 

Fig. 81. Aloysia citriodora: circumnutation of stem, traced from 8.20 A.M.

on March 22nd to 4 P.M. on 23rd. Plant kept in darkness. Movement magnified about 40 times.

 

(16.) Verbena melindres (?) (a scarlet-flowered herbaceous var.) (Verbenaceae).—A shoot 8 inches in height had been laid horizontally, for the sake of observing its apogeotropism, and the terminal portion had grown vertically upwards for a length of 1 � inch. A glass filament, with a bead at the end, was fixed

 

Fig. 82. Verbena melindres: circumnutation of stem in darkness, traced on vertical glass, from 5.30 P.M. on June 5th to 11 A.M. June 7th. Movement of bead magnified 9 times.

 

upright to the tip, and its movements were traced during 41 h. 30 m. on a vertical glass (Fig. 82). Under these circumstances the lateral movements were chiefly shown; but as the lines from side to side are not on the same level, the shoot

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must have moved in a plane at right angles to that of the lateral movement, that is, it must have circumnutated. 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 (Ceratophylleae, 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 200o in 6 h., and in one instance through 220o in 3 h. They generally bent from right to left in the morning, and in an opposite direction in the afternoon; but the movement was sometimes temporarily reversed or quite arrested. It was not affected by light. It does not appear that M. Rodier made any diagram on a horizontal plane representing 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 m�rithalles sup�rieurs, qu’il se propage ensuite, en s’amoindrissant du haut en bas; tandis qu’au contraire le movement de redressement commence par la partie inf�rieur pour se terminer a la partie sup�rieure qui, quelquefois, peu de temps avant de se relever tout � fait, forme avec l’axe un angle tr�s aigu.”

 

(18.) Coniferae.—Dr. Maxwell Masters states (‘Journal Linn. Soc.,’ Dec.

2nd, 1879) that the leading shoots of many Coniferae during the season of their active growth exhibit very remarkable movements of revolving nutation, that is, they circumnutate. We may feel sure that the lateral shoots whilst growing would exhibit the same movement if carefully observed.

 

* ‘Comptes Rendus,’ April 30th, 1877. Also a second notice published separately in Bourdeaux, Nov. 12th, 1877.

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(19.) Lilium auratum (Fam. Liliaceae).—The circumnutation Fig. 83. Lilium auratum: circumnutation 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 the 15th, and the movements during this interval of 18 h. 15 m. are represented by a long broken line. Diagram reduced to half original scale.

 

of the stem of a plant 24 inches in height is represented