PLANT GROWTH

Press, Volume LXXII, Issue 21802, 6 June 1936, Page 13

PLANT GROWTH

EFFECT OF ARTIFICIAL LIGHT

AN INTERESTING LOCAL EXAMPLE

For many years, botanists and agriculturists have been experimenting with the possibilties of the use of artificial lights in the cultivation of plants and trees. In the very heart of the city can be found an example of how an electric light can prove beneficial to trees.

In Victoria square, there are some silver trees round a triangle of grass which surrounds the statue of Queen Victoria. Also on the footpath on this triangle are some powerful standard lamps which were erected there by the Municipal Electricity Department,' 1 the rays of which strike on to some of the branches of the t?ees. It is very noticeable that on the side cf the trees which are near these lights, the leaves have not yet fallen, and in some cases, have retained their green colouring. It is only on the branches of the trees near the lamps that the leaves remain. Experiments Overseas When this interesting observation was brought yesterday afternoon to the notice of Mr L. W. McCaskill, lecturer in biology at the Christchurch Training College, he said that in the the light of experiments conducted during the last few years, it would appear that the standard lights were prolonging the growing period of the silver birches. It would be interesting, he continued, to observe whether deciduous trees, as a whole, kept their leaves longer when placed near an artificial light. Many experiments had been carried out overseas in the use of artificial light in greenhouse culture, for example, for forcing lettuce, endive, radish, and certain flowers. In such experiments, the artificial light had been employed usually at night, said Mr McCaskill, or in some cases had been used to supplement the daylight. Mr McCaskill continued that by use Of a protected electric arc lamp a man had been able to hasten the growth of lettuce by two weeks. The naked electric arc lamp, however, yielded light distinctly injurious to most plants. Continuous night illumination with the electric arc might promote more rapid growth in some plants, but with others there was a tendency for plants to run to seed. The ordinary incandescent electric light, which was fairly rich in red rays, had been successfully employed in forcing lettuce plants to maturity. By the use of acetylene light it was found possible to force the growth of radish and lettuce plants, but more especially flowers like lilies. Length of the Day The striking effect of the length of day on times of flowering and fruiting in plants was demonstrated by two botanists. Garner and Allard, in experiments between 1920 and 1925, continued Mr McCaskill. They showed that plants could be divided into two classes —“long-day” plants, which flowered only when exposed to long hours of daylight, and “short-day” plants, which flowered only when the hours of daylight were short. The “short-day” plants flowered normally in spring or autumn, and included the soya bean, tobacco runnerbean, many ornamental trees (including those of the silver birch variety, like those in Victoria square), and flowers like dahlias and chrysanthemums. The flowering of these plants was retarded or prevented by increasing the length of daylight, said Mr McCaskill. Tnus by the aid of electric light plants have been grown to giant size without flowering; on the other hand, premature flowering was induced by shortening the daylight period. The “long-day” plant: flowered normally in the long summer days, he continued, and included most of the agricultural crops of temperate latitudes, cereals, grasses, clovers, and other species. When exposed to a short day, their vegetable growth increased and flowering was delayed. The intensity of the light seemed to be unimportant, relativ ;ly weak electric light being sufficient to produce the phenomena.