The Movements and Habits of Climbing Plants. Чарльз Дарвин

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СКАЧАТЬ eastern growth commenced, the shoot would be drawn from the stick, and its weight coinciding with the effects of the changed surface of growth, would cause it suddenly to fall to the opposite side, reassuming its previous slight inclination; and the ordinary revolving movement would then go on as before. I have described this curious case with some care, because it first led me to understand the order in which, as I then thought, the surfaces contracted; but in which, as we now know from Sachs and II. de Vries, they grow for a time rapidly, thus causing the shoot to bow towards the opposite side.

      The view just given further explains, as I believe, a fact observed by Mohl (p. 135), namely, that a revolving shoot, though it will twine round an object as thin as a thread, cannot do so round a thick support. I placed some long revolving shoots of a Wistaria close to a post between 5 and 6 inches in diameter, but, though aided by me in many ways, they could not wind round it. This apparently was due to the flexure of the shoot, whilst winding round an object so gently curved as this post, not being sufficient to hold the shoot to its place when the growing surface crept round to the opposite surface of the shoot; so that it was withdrawn at each revolution from its support.

      When a free shoot has grown far beyond its support, it sinks downwards from its weight, as already explained in the case of the Hop, with the revolving extremity turned upwards. If the support be not lofty, the shoot falls to the ground, and resting there, the extremity rises up. Sometimes several shoots, when flexible, twine together into a cable, and thus support one another. Single thin depending shoots, such as those of the Sollya Drummondii, will turn abruptly backwards and wind up on themselves. The greater number of the depending shoots, however, of one twining plant, the Hibbertia dentata, showed but little tendency to turn upwards. In other cases, as with the Cryptostegia grandiflora, several internodes which were at first flexible and revolved, if they did not succeed in twining round a support, become quite rigid, and supporting themselves upright, carried on their summits the younger revolving internodes.

      Here will be a convenient place to give a Table showing the direction and rate of movement of several twining plants, with a few appended remarks. These plants are arranged according to Lindley’s ‘Vegetable Kingdom’ of 1853; and they have been selected from all parts of the series so as to show that all kinds behave in a nearly uniform manner. [24]

      The Rate of Revolution of various Twining Plants.

      (Acotyledons.)

      Lygodium scandens (Polypodiaceæ) moves against the sun.

	H.	M.
June 18, 1st circle was made in	6	0
18, 2nd	6	15	(late in evening)
19, 3rd	5	32	(very hot day)
19, 4th	5	0	(very hot day)
20, 5th	6	0

      Lygodium articulatum moves against the sun.

	H.	M.
July 19, 1st circle was made in	16	30	(shoot very young)
20, 2nd	15	0
21, 3rd	8	0
22, 4th	10	30

      (Monocotyledons.)

      Ruscus androgynus (Liliaceæ), placed in the hot-house, moves against the sun.

	H.	M.
May 24, 1st circle was made in	6	14	(shoot very young)
25, 2nd	2	21
25, 3rd	3	37
25, 4th	3	22
26, 5th	2	50
27, 6th	3	52
27, 7th	4	11

      Asparagus (unnamed species from Kew) (Liliaceæ) moves against the sun, placed in hothouse.

	H.	M.
Dec. 26, 1st circle was made in	5	0
27, 2nd	5	40

      Tamus communis (Dioscoreaceæ). A young shoot from a tuber in a pot placed in the greenhouse: follows the sun.

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	H.	M.
July, 7, 1st circle was made in	3	10
7, 2nd	2	38
8, 3rd	3	5
8, 4th	2	56
8, 5th	2	30
8, 6th	2