Schleiden demonstrated that plant tissues are made up of and developed from groups of cells, of which he recognized the “cytoblast” or cell-nucleus. He observed with great accuracy certain other activities of the cell, and is an important figure in the development of the cell theory. In keeping with other scientists of his time, he held that young cells develop spontaneously from the cytoblast, an acceptance of the theory of spontaneous generation. English translation (Sydenham Society) 1847.