Editing August Weismann (section)

=== German work on cells ===
[[File:Weismann's Germ Plasm.svg|thumb|upright=1.5|Weismann's [[germ plasm]] theory. The hereditary material, the germ plasm, is transmitted only by the [[gonad]]s. Somatic cells (of the body) [[embryology|develop afresh]] in each generation from the germ plasm.]]

Weismann's work on the demarcation between germ-line and soma can scarcely be appreciated without considering the work of (mostly) German biologists during the second half of the 19th century. This was the time that the mechanisms of cell division began to be understood. [[Eduard Strasburger]], [[Walther Flemming]], [[Heinrich Wilhelm Gottfried von Waldeyer-Hartz|Heinrich von Waldeyer]] and the Belgian [[Edouard Van Beneden]] laid the basis for the cytology and cytogenetics of the 20th century. Strasburger, the outstanding botanical physiologist of that century, coined the terms [[nucleoplasm]] and [[cytoplasm]]. He said "new cell nuclei can only arise from the division of other cell nuclei". Van Beneden discovered how chromosomes combined at [[meiosis]], during the production of [[gametes]], and discovered and named [[chromatin]]. Walther Flemming, the founder of [[cytogenetics]], named [[mitosis]], and pronounced "omnis nucleus e nucleo" (which means the same as Strasburger's dictum). The discovery of mitosis, meiosis and chromosomes is regarded as one of the 100 most important scientific discoveries of all times,<ref>[http://carnegieinstitution.org/cover/top_100/ 100 Greatest Discoveries – Carnegie Institution] {{webarchive|url=https://web.archive.org/web/20070927070422/http://carnegieinstitution.org/cover/top_100/ |date=2007-09-27 }} at carnegieinstitution.org</ref> and one of the 10 most important discoveries in [[cell biology]].<ref>[http://science.discovery.com/convergence/100discoveries/big100/biology.html The Science Channel :: 100 Greatest Discoveries: Biology] {{webarchive|url=https://web.archive.org/web/20061024155730/http://science.discovery.com/convergence/100discoveries/big100/biology.html |date=2006-10-24 }} at science.discovery.com</ref>

Meiosis was discovered and described for the first time in [[sea urchin]] [[egg (biology)|eggs]] in 1876, by [[Oscar Hertwig]]. It was described again in 1883, at the level of chromosomes, by Van Beneden in ''[[Ascaris]]'' eggs. The ''significance of meiosis for reproduction and inheritance'', however, was first described in 1890 by Weismann, who noted that two cell divisions were necessary to transform one diploid cell into four haploid cells if the number of chromosomes had to be maintained. Thus the work of the earlier cytologists laid the ground for Weismann, who turned his mind to the consequences for evolution, which was an aspect the cytologists had not addressed.<ref>Although, of course, [[Ernst Haeckel]] had; but he was not a cytologist.</ref> All this took place before the rediscovery of the work of Mendel.