Berries of Vitis vinifera, cvv. Muscat Gordo Blanco and Doradillo, were measured at close intervals (during the day or daily) sequentially while on the vine. Measurements of berry diameter and deformability showed that : (a) There were large diurnal fluctuations due to a decrease in diameter and an increase in softening during the day, both recovering by nightfall. (b) There was a prolonged and steady increase in diameter of 0.043 mm day-1, which was ended by a spurt of growth (an increase of about 0.25 mm during one day), followed then by a second prolonged increase at a new rate of 0.090 mm day-1. (c) Softening, as revealed by deformability, which was initially low, was heralded by a sudden increase followed by a steady daily increase for more than a week. (d) The increase in deformability usually, though not always, preceded the increase in diameter, the median difference being 6 days. (e) There was no evidence of a relationship between the time of softening and vascular proximity of berries on the bunch.

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