Cell theory states that: All living things are made up of cells.
Schleiden was the first to recognize that all plants, and all the different parts of plants, are composed of cells.
Schwann, who came to similar conclusions while studying animal tissues.
The word cell is derived from the Latin word “cellula” which means “a little room”.
It was the British botanist Robert Hooke who, in 1664, while examining a slice of bottle cork under his microscope (later named as compound microscope), found its structure resembling the box–like living quarters of the monks in a monastery, and coined the word “cells”. Cell theory refers to the idea as cells are the basic unit of structure of life. Development of this theory during the mid 17th century was possible by advances in microscopy. The theory states that new cells are produced from other existing cells, and the cell is a fundamental unit of structure, function and organization in all living organisms. Hooke's description of these cells which were actually non–living cell walls was published in his book called Micrographia. His cell observations gave no indication of the nucleus and other organelles found in most living cells.
All cells come from pre-existing cells.
This paved the way for wide acceptance that a hidden world existed just beyond the limits of human vision and encouraged many scientists to take up the microscope in their investigations. One such scientist was German botanist Matthias Jakob Schleiden (1804–1881), who looked at numerous plant samples. Schleiden was the first to recognize that all plants, and all the different parts of plants, are composed of cells. Schwann, who came to similar conclusions while studying animal tissues, quickly saw the implications of their work. In 1839, he published “Microscopic Investigations on the Accordance in the Structure and Growth of Plants and Animals,” which included the first statement of the cell theory: All living things are made up of cells.
Then, in 1858, Rudolf Virchow (1821–1902) extended the work of Schleiden and Schwann by proposing that all living cells must rise from pre–existing cells. This was a radical idea at the time because most people, scientists included, believed that non–living matter could spontaneously generate living tissue. The inexplicable appearance of maggots (larva of a fly) on a piece of meat was often given as evidence to support the concept of spontaneous generation. But a famous scientist by the name of Louis Pasteur (1822–1895) set out to disprove spontaneous generation with a now–classic experiment that both firmly established the cell theory beyond doubt and solidified the basic steps of the modern scientific method.