The following is said to be an infallible sign of a ripe watermelon, it takes close inspection to find sometimes, but the sign is there if the condition for it exists. When the flesh of the melon changes color and its seeds begin to turn black a small scale or blister appears on the rind. They increase in number and size as the melon ripens, until a ripe one shows them thickly strewn over the surface. A small crop of blisters indicates unripe fruit. A melon must be served ice cold. Cut it through the middle, scoop out the flesh with a tablespoon in a circle as much as possible that the pieces may be conical or egg shaped. Cover the platter with grape leaves and pile the fruit upon them, allowing the tendrils of the grapes to wander in and out among the melon cones.
Vaughan's Vegetable Cook Book (1919).