IN TOUCH WITH NATURE

Otago Witness, Volume 1851, Issue 3809, 15 March 1927, Page 5

IN TOUCH WITH NATURE

THE TENDRIL-BEARERS.

(By

J. Drummond,

F.L.S., F.Z.S.)

Mr J. B. Davey, Pirongia, near Te Awamutu, Waikato, is lost in wonder at the climbing devices of the passion fruit, the grape-vine, and other climbers. They seem to him to border on the marvellous. He compares the 'endrils to spiral springs .invented by man, but states that they go one better. The double spirals are the particular objects < f his admiration. He suggests that the spirals, twisting first in one direction, and then in the opposite direction, have been developed in order to reduce the G'pdril's "risk of breaking when it is subjected to strain. The same explanation has been set out clearly by Mr R.. M. Laing, Christchurch. When a tendril i$ twisted in an equal number of twists in opposite directions, he states, it may be pulled straight without leaving any kinks.' When a continuous spiral is straightened kinks remain in it, and - a break may occur at any of them. In a strong wind, a continuous spiral will break, while a plant with tendrils in reversed spirals will ride out the gale with a long range of cable paid out. Mr Davey’s amazement at these devices is shared by the greatest botanists. Amongst these is Charles Darwin, who found that the passion flower exceeds all other climbing plants in the rapidity of its movements and all.other tendril-bearers in sensitiveness of its tendrils. On a passion flower watched by Darwin the internode—the part between the stem and a node—made three revolutions, following the sun, at an average rate of one hour four minutes. The average rate of six revolutions was one hour one minute. A half-grown tendril was not ‘sensitive, but almost fully-grown ones were very sensitive. A single delicate touch on the concave surface of the tip soon caused it to curve. ' A loop >f soft thread that weighed one-thirty-second of a grain,. placed very gently on the tip, caused it to curve thrice; a piece of thin wire, which weighed onefiftieth of a grain, caused it to bend twice. Darwin took hold of the lower part of several tendrils and touched their tips with a thin twig, and watched them through a lens. The tips bega- to bend in 31, 25, 32, 31, 28, 39. 31, and 30 seconds; the movement was. generally perceptible in half a minute, after the touch but once it was clear after 25 sec ids. . 011 several occasions Darwin went out in- a gale to observe a bryony that grew in a hedge, with its tendrils attached to bushes. As the thick or thin branches were tossed to and fro by the wind the attached tendrils, if they had not been very blastic, would have been torn off and the plant been thrown prostrate; but the bryony safely rode out the gale, like a ship l with two anchors down,, and with a long range of cable ahead to serve as a spring as she surges to the storm.

The revolving motion of some tendrils is accelerated or retarded in moving to or fronrithe light; others are indifferent to the : action of light; others move from light to the dark. Tendrils, soon after they catch a support, become much stronger and thicker, sohietimes to a wonderful degree, durable, showing the extent of 'change in their internal tissues. Tendrils ' that fail to catch any object soon shrink and wither; with some plants, they fall off like leaves in autumn. Another botanist, Dr .MacGregor Skene, explains that the coiled part of a tendril, when it has grasped a support, hardens, becomes woody and takes a firm hold. The long straight part, between the. support and the base of the tendril, twists into a tight corkscrew reversed once or twice—in the same way as a thread fixed at both ends cannot be forced into a spiral without at least one reversal in the direction of the twist—and then becomes woody.

One of New Zealand’s loveliest flowers, the common forest clematis, has tendrils so sensitive that if they are stroked with a straw .ever so lightly for a few minutes they gradually bend down and begin to encircle it. Miss Marguerite M. Crookes explains the success of the clematis in its climbing efforts by its use of mechanical devices biased on the same principles as human engineers follow when they wish to combine strength with great flexibility. It uses the cable method. A cross-section of the stem of the clematis, under the microscope, is found to have the strong woody .tissue split into many strands, united by softer tissue, instead of being a solid mass. _ Around the outside of the stem there' is a continuous ring of very strong tissue. This protects the stem from the danger of too much • pressure on account of the growth of the support.

The Hon. G. M, Thomson, iilwavs clear and interesting, has described a breath of wind moving the young stalks of a clematis against the twigs of a tree or other support, and the stalks bending in that direction and grasping the support. Having taken hold, they soon thicken and strengthen their tissues, in response, he states, to a law, which seems ,to be common to all living organisms,, and .which causes-.them to develop new tissues wherever the 1 stimulus of friction or irritation occrirs. When the stem of a clematis is. cut - through with a sharp knife, and when the cut end is examined with a good pocket-lens, it. is seen that the tissues consist of many wedge-shaped bundles of tubes that radiate from a small central piece of pith. ■ The bundles of tubes may not be very beautiful, but they imply a combination bf great strength and elasticity. The. tubes are open conduits, up which, the clematis draws its liquid nourishment. Their size and numbers explain how a plant with a comparatively slender stem grows sufficiently long to produce flowers at the’ top of a* tree perhaps 100 ft high. The clfimatis. sometimes climbs by twining. It relies mainly on its tendrils, but there is evidence that its ancestors were twiners, and that it has developed-the better;method of tendril-bearing, which - ranks amongst the most perfect devices known,..

The .hop, a notable twiner, although not a- tendril-bearer, always twines to ■ the right, in the same direction ,as ; the ; hands of a The convolvulus always, twines to the left. Nothing will coerce these twiners from twining in the direction they

wish, a direction which, perhaps, is dictated by an. inherited tendency, passed from generation to generation. Men of science seem to have irot no nearer explaining why different directions should be preferred than that the preference is caused by causes, by the peculiar con stitution of the living protoplasm in each plant. A strange habit of climbing plants is called circumnutation. It- is a ceaseless searching for a support. A stem goes around and - around, reaching further out every time the circle is comnleted. The tip of the stem of a hop 14 inches long has swept in a circle 19 inches in diameter. The hop is helped in its climbing by many anvil-shaped hooks on tbe ridges of its branches. A tropical plant, Asclepiad, which stood on Darwin’s study table, had a shoot that wept a grand circle five feet in diameter, night and day. in search of an object round which *to ’ twine. The Kie-Kie, whose name is corrupted into “g’ay-gay” -in some districts, is one of the root-climbers. Fixing its roots into crevices in the bark of other plants, it pulls itself up. Several of the ratas ascend by using rootlets. The bush lawyer uses hooks, like recurved claws.

Blooming in bogs and peat in quiet, secluded places on New Zealand mountains, there is a plant as pretty as it is modest. It is not uncommon in alpine bogs, but it never fails to attract the attention of people who go. up into those district. In the first place, it is conspicuous on* account of the large compact cushion formed by its. densely tufted stems and its thick, bright, shining leaves, a lovely emerald green. Its greatest beauty is .in its little white starry flowers, snug amongst the upper-most leaves. It favours places from 3000 to 6000 feet above sea-level, but on Stewart Island it descends almost to the sea-level. ’ The latest report of its charming presence is from the Rough Peaks Range, about nine miles froni Collins Bay, Lake akatipu. Messrs- G.- Simpson and J. Scott Thomson saw it there when they explored the range in March last year. Amongst jjs companions were Wild Spaniards, mountain daisies, ourisias, and gentians. It has no popular name. Officially, it. is Dona.tia novae-zelandiae. It is not lavish with its charms. New Zealand and Tasmania are the only countries it graces, and the only other species in the genus is a native of Fuegia, far south in South America.