Roots - Kakon

The term refers to the single or multicellular thread-like root-like part that grows on the surface of plants and fungi that do not have roots, such as algae, mosses, and the prothallus of ferns. It is structurally similar to the root hairs of vascular plants and has the functions of absorption and fixation. In algae, there are those with complex protruding single-cell structures, such as Balloon Flower, and those with multicellular branching structures, such as Charophytes. In brown algae, rhizoids gather together to form an adhesive organ like the roots of vascular plants, but this is a pseudotissue and does not show tissue differentiation such as vascular bundles. Single-celled rhizoids grow on the underside of the gametophyte of Marchantiales, and one-cell row of rhizoids grows at the base of the stem-like part in Polytrichum. The underside of the base of the prothallus of ferns has a rhizoid consisting of a single cell or two or three cells. The rhizoids of lichens are hyphae that grow out of the cortex on the underside and act as an adhesive, but they are called rhizoid hyphae to distinguish them from the hyphae of the medulla and cortex. In fungi, hyphae that act as anchors, such as those seen in Rhizopus, are called rhizoids.

[Eimasa Nishino]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

藻類、コケ植物、シダ植物の前葉体など根をもたない植物や菌類の表面に生じる単細胞または多細胞の糸状の根状部をさすが、構造的には維管束植物の根の根毛に類似し、吸収、固着の機能をもつものをいう。藻類ではフウセンモのように単細胞の一部が複雑に突出した形、車軸藻(しゃじくも)類のように多細胞で分枝した形のものがある。褐藻類では仮根が集まって維管束植物の根のような吸着器官をつくるが、これは偽組織で、維管束などの組織分化はみられない。ゼニゴケ類の配偶体の裏面には単細胞の仮根ができ、スギゴケ類では茎状部の基部に1細胞列の仮根ができる。シダ植物の前葉体の基部の下面には単細胞または2、3の細胞からなる仮根がある。地衣類の仮根は下面の皮層から出た固着の働きをする菌糸をさすが、髄層や皮層の菌糸と区別してとくに仮根菌糸とよばれる。菌類ではクモノスカビにみられるような固着の働きをする菌糸を仮根とよぶ。

［西野栄正］

出典　小学館　日本大百科全書(ニッポニカ)日本大百科全書(ニッポニカ)について　情報 | 凡例