Who realized that cells were the units that make up plants?

The realization that cells are the fundamental units that make up plants is attributed to the German botanist Matthias Schleiden. In 1838, Schleiden proposed that all plant tissues are composed of cells, contributing to the development of the cell theory alongside Theodor Schwann, who later extended this concept to animals. Their work laid the foundation for modern Biology by establishing that cells are the basic building blocks of all living organisms.