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 (prō-thăl′əs) or pro·thal·li·um (-thăl′ē-əm)
n. pl. pro·thal·li (-thăl′ī) or pro·thal·li·a (-thăl′ē-ə)
A small, flat, delicate structure produced by a germinating spore and bearing sex organs. It is the gametophyte of ferns and some other plants.

[New Latin : pro- + Greek thallos, shoot (from thallein, to sprout).]

pro·thal′li·al (-lē-əl) adj.


(prəʊˈθæləs) or


n, pl -li (-laɪ) or -lia (-lɪə)
(Botany) 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
[C19: from New Latin, from pro- before + Greek thallos a young shoot]
proˈthallic, proˈthallial adj


(proʊˈθæl i əm)

n., pl. -thal•li•a (-ˈθæl i ə)
the gametophyte of ferns and related plants.
[1855–60; < Greek pro- pro-2 + thallíon, diminutive of thallós young shoot; see -ium2]
pro•thal′li•al, pro•thal′lic, pro•thal′line (-ˈθæl in, -aɪn) adj.
pro•thal′loid, adj.
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References in periodicals archive ?
This was an ephemeral phase, as it quickly underwent longitudinal divisions in all the cells, including the apical one, arising bidimensional prothalli around 12 days after germination (Fig.
Morphology of spores and prothalli of some species of Polypodiaceae.
Farlow (1874) reported the development of fern plantlets directly from prothalli, without the production and fertilization of an egg (apogamy = without sexual union).
Spores will take 2 to 6 weeks to germinate, but when they finally do, you will observe the green, somewhat slimy-looking, prothalli.
Sporangia are produced in most ferns on the underside of the leaves, which is again comparable with the position of gametangia on the underside of the prothalli, where archegonia develop near the growing blastozone (Figs.
Later, middle apical cell divides to generate a meristematic zone, slightly lateral in position, and because of this, prothalli become clearly asymmetric.