The structure that forms right down the middle of a dividing plant cell is called the cell plate.

Here's why:

* Cell Division in Plants: Plant cells divide by a process called cytokinesis, which happens after the nucleus has divided (mitosis or meiosis).

* Cell Plate Formation: During cytokinesis, small vesicles (membrane-bound sacs) from the Golgi apparatus migrate to the center of the dividing cell. These vesicles fuse together to form a disk-like structure called the cell plate.

* Cell Wall Formation: The cell plate grows outward, fusing with the existing cell wall at the edges. The cell plate eventually becomes a new cell wall, dividing the original cell into two daughter cells.

So, the cell plate is essentially the foundation for the new cell wall that separates the two daughter cells.