Cellular theory , ∨ Cell theory Meaning, Definition & Usage

Definitions
  1. (Biol.), a theory, according to which the essential element of every tissue, either vegetable or animal, is a cell; the whole series of cells having been formed from the development of the germ cell and by differentiation converted into tissues and organs which, both in plants ans animals, are to be considered as a mass of minute cells communicating with each other.

Webster 1913