THE FALLING LEAF

Otago Daily Times, Issue 23500, 14 May 1938, Page 22

THE FALLING LEAF

SOMETHING OF ITS MEANING We speak of the falling ot leaves from trees, shrubs, and all kinds of deciduous plants as being the visible sign of the passing of autumn and approach of winter. This year we have witnessed a good deal of variation from the normal procedure The drought that extended from midsummer far into autumn caused an unusual amount of April leaf-falling, and we heard predictions of an early and bad winter. Close examination ol those leaves that fluttered to earth so soon revealed the fact that they were not really matured; they fell because moisture was scarce, and something had to be done to economise water. Every leaf on a tree or shrub not only uses up a certain amount of moisture for its own sustenance, but exudes a surplus which passes away into the atmosphere. It was part of Nature’s method of counteracting the evil effects of the drought to reduce the number of leaves that could absorb and disperse moisture. RAIN CAUSES CHANGES

Then came rain, and with the replenishment of moisture supplies, Nature changed her tactics, and kept the younger foliage on trees and shrubs growing longer than usual. Thus it has happened that, although some leaves have fallen with every gust of wind, many have remained on the trees well into May, and, although somewhat later than usual, we have been treated to a gorgeous panorama of brilliant autumn tints which have lit up not only gardens, but the roadsides and woodlands of the country in a manner that has made it a ,ioy to leave an office and go roaming. This annual shedding of foliage is a matter of great importance to a tree. All through the growing season every leaf has its share to perform in the work of absorbing from the atmosphere vapours which are required to combine with the juices taken up by the roots from the soil in order that all may be converted into plant food. At night, respiration through the leaves returns to the atmosphere certain gaseous vapour and moisture the tree does not utilise. During the whole period of active growth, this process goes on, the leaves and roots acting in co-operation, put, despite the. respiration of the foliage there accumulates in the cellular structure of the tree a certain amount of surplus or unwanted material which must be expelled before it reaches a stage which would be toxic or poisonous to the tree. Thus it happens that, when the season’s growth is about complete, the leaf cells become filled with this unwanted material, extracted from the wood cells. As the leaves become thus filled, they lose their summer green and assume different colours, and when they reach the stage that they can hold no more, they fall from the tree, taking their load of waste matter with them. In some cases the fall cannot happen until frost has its contraction and expansion effect upon the fibres and tissues of the leaves. That is why foljage has remained so long on the branches and twigs this autumn. Evergreens hold their old leaves until next year’s young foliage has developed: thus we find hollies, laurels, rhododendrons, and conifers shedding foliage in spring instead of autumn, keeping the plants continuously furnished instead of sometimes bare. Although leaves, when they fall, are charged with materials the plant does not want, as we have already remarked, those leaves, placed in a heap and allowed to ferment and decompose, will be converted into serviceable humus-forming leaf mould. That which was likely to become poisonous if allowed to remain in the limbs of the tree undergoes chemical changes during the decomposition process, wbich make it hramless and even beneficial to the root system another year. This fall of the leaf is one among the many instances which go to prove that Nature does not work in a haphazard manner, but that into each phenomenon, perhaps primarily designed to achieve one major object—as in this instance to prepare a tree or shrub for rest—is also utilised on a sound economic basis to serve some other but useful purpose.