NATURALISTS’ FIELD CLUB

Evening Star, Issue 19856, 3 May 1928, Page 2

NATURALISTS’ FIELD CLUB

INDOOR MEETING Despite the boisterous weather, there was a very large attendance of members at the indoor meeting field on Monday evening to hear a lecture by tho club’s patron, the Eon. G. M. Thomson, whose subject was ‘ Movements in Plants.’ It was stated that many plants have power of movement, though as yet, no satisfactory explanation has been given of the direct cause, but in many instances it is due to external influences. Motion in entire plants occur in Oscillaria, Diatoms, and some other forms of lower Algae. Power of movement is characteristic of Protoplasm, a substance found in all living cells. Protoplasm in plants is always in motion, but as it is enclosed in cell walls of cellulose, the movement is mot always* seen. Nitella, a pretty Ifttle green water plant which may be- found in the Silverstream water race, has long narrow cells forming filaments, and under'the microscope one is able to see the protoplasm streaming round and round in the cells. Naked masses of protoplasm such as mycomycetes—a group of organisms lower than frogi, possess great power of locomotion. This may be seen in certain pits where masses creep over tho partitions fiom pit to pit. Inflipnce of light or change of temperature inay induce movement in plants. Green algae in wator < will' move in obedience to the laws of light. Plants in a room grow to tho light, while climbing shoots of ivy and tendrils of Virginian creeper turn from the light. Certain leaves and petals of flowers change their position under the influence of light. In leaves these periodical movements consist in tho closing _up of such organs towards the evening and their expansion in the daylight. In tho petals of flowers great differences occur in different plants, some opening or closing at particular hours of the day. This periodical closing up of leaves and flowers has been called the sleep of plants. The compound leaves of certain fcguminosac and oxalidacea are marked illustrations of these periodical movements. The oxalis, commonly known as shamrock and some species of clover, in strong sunlight present the edge of the leaf instead of tho surface, to the sky. Darwin thought this was to protect the chlorophyll from too intense light. At night the leaflets of trifolium. vicia, lathyrus, etc. fold up. Those of lupins, phaseolus (scarlet runner), fold down. The object of these movements is apparently to diminish radiation and thus prevent injury from excessive fall of temperature. Similarly, flowers are affected. Anagallis nrvensis (pimpernel) or poor man’s weather glass, for example, opens by day to attract insects, but closes at night or in damp, cold weather, probably to protect the pollen. The florets of the common daisy curve outward in the morning and close in the evening. Change of temperature does not induce movement, it only modifies its activity. Flowers of tulip, crocus, etc. open with the rise of temperature and close with its fall. Experiment may be made with these flowers by bringing thorn, when closed, from a chilly atmosphere into a warm room, when it will be noticed that they will eventually reopen. Then there are the distinctive movements of climbing plants. This may bo noticed particularly in some quick-growing twiners. The young growing shoots of the hop are continually turning round and round. The hop vine moves with the sun, and when it comes in contact with something rigid, it seizes it for support. Clematis, scarlet runners, convolvulus, are also good examples. Individual climbing plants have distinctive methods of direction; some leaf climbers, such as clematis and tropaeolum will respond to irritation Movements of irritability are also con-1 nected with the fertilisation of flowers. ! The irritability may bo caused by in-1 sects entering the flowers as is il-1 Instratod by some of our local orchids. Mr Thomson illustrated his lecture throughout with specimens of the plants mentioned, and at its conclusion j he was accorded a very hearty vote of thanks.