The part of the plant that is needed to develop into a fruit is the ovary.

Here's why:

* Ovary: The ovary is the base of the flower and contains the ovules, which are the female reproductive cells.

* Fertilization: When a pollen grain from the male part of the flower (the stamen) reaches the ovary and fertilizes the ovule, the ovule develops into a seed.

* Fruit Development: The ovary itself, after fertilization, begins to swell and develop into the fruit.

So, the fruit is essentially a mature ovary that encloses and protects the seeds.