Who is known for stating that all plants are made of cells?

Matthias Schleiden is recognized for stating that all plants are made of cells, which is a foundational concept in cell theory. In the mid-19th century, he, along with Theodor Schwann, who focused on animals, proposed that all living organisms are composed of cells, establishing a critical principle in biology. Schleiden's work specifically emphasized the cellular composition and structure of plant tissues, contributing to the understanding of plant biology and the broader implications of cell theory in the study of life. This concept laid the groundwork for further investigations into cellular function and the interrelation between cells in various organisms.