Lavender Berries are a rare fruit that grow only on Pessim's Island.
They grow on a bush and are about the size of a gooseberry, and are of a lovely lavender color. Eating a lavender berry causes one to shrink to the size of an insect. The only remedy is to eat one of the Dark Purple Berries.
Pessim discovered the unusual properties of these berries after his neighbors deserted him on the island.
When it was time to leave the island, Trot and Cap'n Bill ate of the Lavender Berries so they could be carried away by the flying Ork, bringing Dark Purple Berries with them so they could be restored. (The Scarecrow of Oz)