A term devised by August Weismann (1834-1914) for a kind of protoplasm in the nuclei of the reproductive or germ cells and tissues of the body, which constituted the hereditary material. It is thus analogous to DNA. He distinguished the germ cells from the soma or somatic cells, which make no contribution to germ plasm during development. The germ plasm was, according to Weismann, was divided into smaller, hierarchical arranged units that control development directly. The smallest units, which he termed biophors and which are analogous to messenger RNA, were depicted as consisting of molecules that were carriers of the ‘quality’ of the cell. The next highest units were determinants made up of a collection of biophors and that in turn formed high-order relationships called ids. The ids were portrayed as being organised into idants, the most complex unit of the germ plasm, and which are approximately the same as chromosomes. Weismann claimed that the idants contained all of the heredity material, but we know now that each chromosome only contains part of the entire genome. Alternative terms for germ plasm are gonoplasm and idioplasm.
See Central dogma of molecular biology, Chromosome, DNA (deoxyribonucleic acid), Germinal (or germ) layers, Modern synthesis, Oocytes, Oogenia, Protoplasm, RNA (ribonucleic acid), Soma (or somatic cells), Theory of the germ plasm