The tiny holes in the cell walls of plants that allow for the passing of materials are called the
middle lamella
plasmodesmata
stomata
stroma

The correct answer for the blank is-

Plasmodesmata .

Plasmodesmata can be described as small channels ( or small holes) in the cell wall of adjacent plant and algal cell.

These channels allow the cytoplasm of adjacent cell to physically communicate with each other, thus allows the transport certain molecules ( such as proteins) from one cell to the adjacent cell through a symplastic pathway ( that is through the cytoplasm of the cells).