1. The percentage loss of moisture from young oranges and grapefruit decreases rapidly as the fruits increase in size. This change doubtless is due largely to the decrease in proportionate surface area as the fruit increases in diameter. 2. Observations on tagged fruits confirm the common knowledge that young citrus fruits readily undergo abscission up to a rather definite stage of size development, but only rarely thereafter. 3. It is possible that evaporation rate is an important factor in determining susceptibility to abscission. 4. Stomatal regulation or the nature of the rind is not an important factor in determining the rate of water loss from detached fruits of different sizes. 5. The size reached by grapefruit before the time of extremely high temperatures may determine to a large extent the occurrence of fruit clusters. Detached citrus fruits of approximately the same size lose their moisture at approximately similar rates. 6. The moisture content is very similar in young orange fruits of differe...