Virchow is the scientist who stated that all cells arise from pre-existing cells. This concept is known as the principle of biogenesis. It is a fundamental principle in biology that states that living organisms can only arise from pre-existing living organisms.

Virchow's contribution to cell theory:
1. Cell Theory: Virchow made significant contributions to the cell theory, which states that all living organisms are composed of cells, and cells are the basic units of structure and function in living organisms. He expanded on the previous work of Matthias Schleiden and Theodor Schwann, who proposed the first two principles of the cell theory.
2. Omnis cellula e cellula: Virchow added the third principle to the cell theory, "Omnis cellula e cellula," which translates to "all cells arise from pre-existing cells." This principle contradicted the widely accepted theory of spontaneous generation, which suggested that living organisms could arise spontaneously from non-living matter.

Evidence supporting Virchow's statement:
1. Observation: Virchow observed and studied cells under a microscope. He observed that cells divide to form new cells during various physiological processes, such as growth, repair, and reproduction.
2. Experimental evidence: Virchow conducted experiments to demonstrate cell division. He observed cell division in various tissues and organisms, including plants and animals. These experiments provided direct evidence that new cells are formed from pre-existing cells.

Significance of Virchow's statement:
1. Disproving spontaneous generation: Virchow's statement played a crucial role in disproving the theory of spontaneous generation, which was widely accepted before the cell theory. His experiments and observations provided evidence that living organisms do not arise spontaneously but from pre-existing cells.
2. Foundation for modern biology: Virchow's statement laid the foundation for the modern understanding of cell biology. It emphasized the importance of cells as the building blocks of life and highlighted the continuity of life through cell division.

In conclusion, Virchow's statement that all cells arise from pre-existing cells is a fundamental principle in biology. His contributions to the cell theory and his experimental evidence played a crucial role in establishing this principle and disproving the theory of spontaneous generation.