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The Collaborative International Dictionary
Rhizoid

Rhizoid \Rhi"zoid\, n. [Gr. ??? root + -oid.] (Bot.) A rootlike appendage.

Douglas Harper's Etymology Dictionary
rhizoid

"root-like," 1858, from Greek rhiza "root," literal and figurative (see rhizome) + -oid. As a noun from 1875.

Wiktionary
rhizoid

n. (context botany English) A rootlike structure in fungus and some plants that acts as support and/or aids the absorption of nutrients.

WordNet
rhizoid

n. any of various slender filaments that function as roots in mosses and ferns and fungi etc

Wikipedia
Rhizoid

Rhizoids are simple hair-like protuberances that extend from the lower epidermal cells of bryophytes, Rhodophytes and pteridophytes. They are similar in structure and function to the root hairs of vascular land plants. Similar structures are formed by algae and some fungi. Rhizoids are formed from single cells, whereas roots are multicellular organs composed of multiple tissues that collectively carry out a common function.

Plants originated in water, from where they gradually migrated to land during their long course of evolution. In water or near it, plants could absorb water from their surroundings, with no need for any special absorbing organ or tissue. Additionally, in the primitive states of plant development, tissue differentiation and division of labor was minimal, thus the requirement for specialized water absorbing tissue was not required. Once plants colonized land however, they required specialized tissues to absorb water efficiently, and also to anchor themselves to the land.

Rhizoids absorb water by capillary action, in which water moves up between threads of rhizoids and not through each of them as it does in roots.

In fungi, rhizoids are small branching hyphae that grow downwards from the stolons that anchor the fungus to the substrate, where they release digestive enzymes and absorb digested organic material. That is why fungĂ­ are called heterotrophs by absorption. In land plants, rhizoids are trichomes that anchor the plant to the ground. In the liverworts, they are absent or unicellular, but multicelled in mosses. In vascular plants they are often called root hairs, and may be unicellular or multicellular.

In certain algae, there is an extensive rhizoidal system that allows the alga to anchor itself to a sandy Substrate from which it can absorb nutrients.

Usage examples of "rhizoid".

The branched filamentous rhizoids which spring from the lower region of the stem also correspond to protonemal branches.

The protonema forms a flat, lobed, thalloid structure attached to the soil by rhizoids, and the plants arise from marginal cells.

Fungal hyphae occur in the rhizoids and in the cells of the lower region of the thallus of many liverworts, as in the endotrophic mycorhiza of higher plants.

A filamentous protonema is first developed, some of the branches of which are exposed to the light and contain abundant chlorophyll, while others penetrate the substratum as brown or colourless rhizoids.

The social growth of the plants characteristic of many mosses is a result of the formation of numerous plants on the original protonema and on developments from the rhizoids.

In the Marchantiales the chief supply is obtained from the soil by the rhizoids, and its loss in transpiration is regulated and controlled.

The living mortar grew between the shades, sending painful rhizoids into any of the unfortunates that stopped moving.