Watermelon fruit is a kind of fruit, fertilized by ovary. The whole fruit consists of peel, pulp and seeds. Among them, the peel develops from the house wall, the pulp develops from the placenta, and the seed develops from the fertilized ovule. The first sentence is correct.
Plum is a fruit, the fruit develops from ovary, and the fertilized egg develops into ovule. The second sentence is wrong.