Robert Hooke named cells after monks' rooms while staring at cork
In 1665 Robert Hooke peered at a paper-thin slice of bottle cork and saw a mass of tiny pores. He called them cells, after the Latin for a small room like a monk's lodging. What he was actually looking at were empty plant walls, and he never guessed the boxes had once been alive.
Hooke described them in Micrographia, a book of 60 detailed observations made with a coarse compound microscope, a device that had first appeared in Europe around 1620. His lenses were too weak to show a nucleus or anything else inside. Examining blue mould on leather, he failed to find seeds and fell back on the ancient idea that life could arise spontaneously from heat.
Anton van Leeuwenhoek, a draper who got hooked on microscopes after seeing one as an apprentice in Amsterdam, did far better. Grinding a tiny glass sphere into a single lens, he reached about 270 times magnification when earlier instruments topped out near 50. In a letter to the Royal Society dated October 9, 1676, he reported moving specks he called animalcules and argued that motion meant life. Curiosity about taste led him to study an ox's tongue and then pepper water, where he found bacteria. He also gave the first accurate description of red blood cells and was first to see sperm cells. Hooke, reading his letters, confirmed observations many contemporaries doubted.
Animal tissue is fragile, so its cells were spotted later than those of plants. In 1839 Matthias Schleiden argued that plants are built from cells, and Theodor Schwann extended the claim to animals, giving the theory its first two pillars. Schleiden's notion that new cells crystallise out of fluid was wrong, and his core idea had been voiced earlier by Barthelemy Dumortier.
The third pillar, that every cell comes from an existing cell, was stated by Rudolf Virchow in 1855 as omnis cellula e cellula. Robert Remak had already published the idea in 1852, and some suggest Virchow plagiarised him. Some biologists still dispute whether the theory covers everything alive, since they regard viruses, which lack cells, as living.
Source: Cell theory
