… In animals, in addition to the above examples of alternating sexual and asexual reproduction, alternation of generations in a broad sense also includes cases where hermaphroditism (reproduction by the union of an egg and sperm) and parthenogenesis (reproduction in which an egg cell becomes a new individual without fertilization) alternate (aphids, water fleas), and alternation of hermaphroditism and larval reproduction (parthenogenesis by larvae) alternate (cecidomy, schistoma). In plants, alternation of generations was first discovered in ferns and mosses by Wilhelm Hofmeister (1824-77) of Germany (1851), and has since been found in many other plant groups. Alternation of generations in plants is often accompanied by a change in the nuclear phase (number of chromosomes), in which the starting point of each generation is the haploidization of cells by meiosis (the number of chromosomes changes from 2n to n ) and the diploidization by fertilization (conjugation) (from n to 2n ). … From [Gymnosperms]…It was R. Brown (1827) who correctly recognized gymnosperms as plants whose seeds (ovules) are not enclosed in carpels (atria) as they are today. In 1851, W. Hofmeister compared the cones of conifers with the sporangia of the Lycopod family and discussed the organological homology between the two. This was the first important achievement in determining the taxonomic position of gymnosperms. … *Some of the terminology that mentions "Hofmeister, W." is listed below. Source | Heibonsha World Encyclopedia 2nd Edition | Information |
… 動物では,有性生殖と無性生殖とが交互に出現する上記のような例のほかに,両性生殖(卵と精子の合一による生殖)と単為生殖(卵細胞が受精を経ないで新個体となる生殖)が交代する場合(アリマキ,ミジンコ),両性生殖と幼生生殖(幼生が行う単為生殖)が交代する場合(タマバエ,ジストマ)なども広い意味の世代交代に含まれる。 植物ではドイツのホフマイスターWilhelm Hofmeister(1824‐77)がシダ植物とコケ植物ではじめて世代交代を発見(1851)したが,その後,他の多くの植物群でも見いだされている。植物の世代交代は同時に核相(染色体数)の交代を伴う場合が多く,その場合は,減数分裂による細胞の単相化(染色体数が2nからnになること),および受精(接合)による複相化(nから2nになること)が,それぞれの世代の起点となる。… 【裸子植物】より…裸子植物を今日のように,種子(胚珠)が心皮(心房)に包まれていない植物として正しく認識したのは,ブラウンR.Brownである(1827)。1851年,ホーフマイスターW.Hofmeisterは球果類の球果とヒカゲノカズラ科の胞子囊穂を比較して,両者の器官学的相同性を論じた。これが裸子植物の分類学的位置を決める最初の重要な業績であった。… ※「Hofmeister,W.」について言及している用語解説の一部を掲載しています。 出典|株式会社平凡社世界大百科事典 第2版について | 情報 |
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