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[proh-thal-uh s] /proʊˈθæl əs/
noun, plural prothalli
[proh-thal-ahy] /proʊˈθæl aɪ/ (Show IPA).
Origin of prothallus
From New Latin, dating back to 1850-55; See origin at pro-2, thallus Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2017.
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Examples from the Web for prothallus
Historical Examples
  • As a rule, too, in the prothallus only one of the archegonia shows any further signs of development.

    How to Know the Ferns S. Leonard Bastin
  • The prothallus is a small underground body destitute of chlorophyll.

    How to Know the Ferns S. Leonard Bastin
  • In the case of L. inundatum the length of time which elapses between the coming of the prothallus is nothing like so great.

    How to Know the Ferns S. Leonard Bastin
  • prothallus, the leaf-shaped green organism that grows from the spore of a fern and produces sexual organs, 49.

  • For a while the newly-born Fern relies upon the prothallus for sustenance, but eventually starts an independent existence.

    How to Know the Ferns S. Leonard Bastin
  • It is on the prothallus, however, that the sexual organs are produced, and after fertilization the plant as we know it arises.

    How to Know the Ferns S. Leonard Bastin
  • Upon the prothallus, or somewhat sunken in it, the sexual organs appear.

    The Nursery Book Liberty Hyde Bailey
  • This filament is the beginning of the body, known as the prothallus, which is responsible for the sex organs.

    How to Know the Ferns S. Leonard Bastin
  • On the under side of the prothallus two kinds of organs appear (Fig. 510).

  • In some of the Lycopodiums the spores have a remarkable habit of resting before the development of the prothallus.

    How to Know the Ferns S. Leonard Bastin
British Dictionary definitions for prothallus


noun (pl) -li (-laɪ), -lia (-lɪə)
(botany) the small flat free-living gametophyte that bears the reproductive organs of ferns, horsetails, and club mosses. It is either a green disc on the soil surface or it is colourless and subterranean
Derived Forms
prothallic, prothallial, adjective
Word Origin
C19: from New Latin, from pro- before + Greek thallus a young shoot
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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prothallus in Science
Plural prothalli (prō-thāl'ī)
The gametophyte of homosporous ferns and some other plants. Prothalli have chlorophyll for photosynthesis, but they are not differentiated into roots, stems, or leaves. They are usually small, flat, and delicate. Prothalli develop from germinated spores, and they bear both archegonia for producing eggs and antheridia for producing sperm. See more at alternation of generations.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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