The cell nucleus is the largest of the membrane-bounded organelles which characterise eukaryotic cells. It is thought of as the control centre since it contains the bulk of the cell’s genetic information in the form of deoxyribonucleic acid (DNA).
The Scottish botanist and paleobotanist Robert Brown discovered the cell nucleus in 1831 while observing cells of orchidaceous plants. In his 1831 publicaton he states, “In each cell of the epidermis of a great plant of this family, especially of those with membranaceous leaves, a single circular areola, generally somewhat more opake than the membrane of the cell, is observable. This areola, which is more or less distinctly granular, is slightly convex, and although it seems to be on the surface is in reality covered by the outer lamina of the cell. There is no regularity as to its place in the cell; it is not unfrequently however central or nearly so.” The “areola” which he observed was the nucleus of the cell. Here is a photomicrograph of onion cells with their round nuclei visible:
- https://books.google.com.pk/books?id=Y0LhlP7eujsC&source=gbs_navlinks_s, page 710.