COLOURING OF GRAPES

New Zealand Herald, Volume XXVII, Issue 8321, 30 July 1890, Page 6

COLOURING OF GRAPES

In a communication to the Botanical Society of Belgium, M. Laurent has recorded some experiments in regard to grape colouring that should Ire interesting to growers of the fruit. These experiments were made in the School of Horticulture at Vilvarde, on Black Hamburgs. When the berries were the size or peas, two bunches were placed in card-board boxes, blackened on the outside, and were allowed to remain there until the berries were ripe. It was found that there wa-r no difference either in flavour or colour of grapes so treated from those grown in the ordinary way. To show that in this experiment the berries received adequate food supply from the leaves, and consequently coloured well, M. Laurent experimented by cutting off the food-supply, by means of the ringing process, from four bunches on the same day that the other bunches were placed in the dark boxes. Two rings of bark, each about a quarter of un inch in depth were taken from the vine, one just above, the other just below the point whence the stalk of the bunch originated, so that the bunch was, in fact, isolated. Of the four bunches so treated two were placed in darkened boxes, two others remained exposed to the light. When the crop was ripe, the bundles which had been subjected to tiiedouble process of ringing and of removal from the light—those, in fact, in which access of food Mas quite prevented—remained green or only slightly coloured, deficient in size, and aeid in flavour. The two bunches which had been subjected to the ringing process, i but which were exposed to the light, pro- ! duced berries nearly of the normal size, some reddish, others green ; the flavour was acid, especially in those that remained green. Similar experiments, had been carried on for three successive years, with the same results. If, however, berries were allowed to get too large before experiments were made, they coloured even after ringing and being placed in the dark. By these experiments M. Laurent has proved that the colouring matter of grapes may bo formed in the absence of light, if the grapes have a sufficient supply of nourishment. It may therefore be surmised that the colouring i matter of grapes arise from a dehydration - of glucose during the last period of maturation. If this bo so, then the want of colour and sweetness in grapes may be due to defective nutrition, due to overcropping, to imperfect exposure to light, and to .shanking. Under each of these circumstances the grapes do not receive a full supply of sugary food, and the colouring matter is diminished in proportion. The deductions of science seem to be that there are two sorts of colouring matter in fruit, the one directly influenced by light, the other only indirectly so. _ On this subject one writer has tire following :—" The action of light in colouring fruits is well known and curious illustrations of it are afforded when an apple, for instance, has been surrounded while growing by a net, the net-work is clearly marked on the ripe fruit, tire position of' the threads being marked by imperfectly coloured lines, while the interspaces to which access of light is nob prevented, are brightly coloured. But while this is the rule in many cases, it is not so in all. The berries of the berberis, of the hawthorns, and of some black grapes, colour as well when shaded by the "foliage as in full sunlight, temperature and other conditions being equal.