In 1838, a German botanist, M.I.Schleiden studied the plant cells and emphasized that "cells are organisms and entire animals and plants are aggregations of these organisms arranged according to definite laws. "In 1839, another German zoologist T. Schwann stated "we have seen that all organisms are composed of essentially like parts namely of cells." The deductions of the two microscopists (Schleiden and Schwann) formed the basis of what came to be known as the cell theory. The cell theory holds that all living matter, from the simplest of unicellular organisms to very complex higher plants and animals, is composed of cells and that each cell can act independently but functions as an integral part of the complete organism.
