The finer points of cellular purpose and composition were not understood form many years, slowly developing as microscopes improved. In fact, the realization that cells were the fundamental unit of plants and animals did not occur until the 1830s. Previously cells had been believed to be simply pores, but the detection of nuclei and moving protoplasm put an end to the misconception. For other discoveries, additional microscopical enhancements needed to be made. Walter Flemming's advanced methods of fixing and staining cells, for instance, facilitated his observation of chromosome transmission between cells and led to his very precise account of mitosis and cell division in 1882.