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The Collaborative International Dictionary
Prothallium

Prothallium \Pro*thal"li*um\, n.; pl. Prothallia. [NL.] (Bot.) Same as Prothallus.

Wiktionary
prothallium

n. 1 A plant, usually a pteridophyte, in gametophyte stage in the metagenesis cycle. 2 The young gametophyte of a liverwort or peat moss.

Wikipedia
Prothallium

A prothallium, or prothallus (from Latin pro = forwards and Greek θαλλος (thallos) = twig) is usually the gametophyte stage in the life of a fern or other pteridophyte. Occasionally the term is also used to describe the young gametophyte of a liverwort or peat moss as well.

The prothallium develops from a germinating spore. It is a short-lived and inconspicuous heart-shaped structure typically 2-5 millimeters wide, with a number of rhizoids (root-like hairs) growing underneath, and the sex organs: archegonium (female) and antheridium (male). Appearance varies quite a lot between species. Some are green and conduct photosynthesis while others are colorless and nourish themselves underground as saprotrophs.

Usage examples of "prothallium".

The beings multiplied by means of spores - like vegetable pteridophytes, as Lake had suspected - but, owing to their prodigious toughness and longevity, and consequent lack of replacement needs, they did not encourage the large-scale development of new prothallia except when they had new regions to colonize.

The beings multiplied by means of spores--like vegetable pteridophytes, as Lake had suspected--but, owing to their prodigious toughness and longevity, and consequent lack of replacement needs, they did not encourage the large-scale development of new prothallia except when they had new regions to colonize.