Why did Robert Hooke call them cells?

Robert Hooke called named cells "cells" because of their similarity to the small rooms in monasteries, also called "cells," in which the monks lived and worked. Hooke first saw cells while examining a specimen of cork with his microscope and was intrigued by the discovery of such structures.

Following his discovery, he began to examine other plants, such as fennel, carrots and ferns, for similar structures, and he counted the structures to determine how many existed in a given area. In 1665, he published a book on microscopy called "Micrographia" that documented these findings. Though his microscope was too crude to see deeply into the cells, he was able to see that they were filled with liquid.