The Collaborative International Dictionary
Prothallus
Prothallus \Pro*thal"lus\, n.; pl. Prothalli. [NL., fr. Gr. ? before + ? a young shoot.] (Bot.) The minute primary growth from the spore of ferns and other Pteridophyta, which bears the true sexual organs; the o["o]phoric generation of ferns, etc.
Wiktionary
prothallus
n. A prothallium.
Usage examples of "prothallus".
Prothallus bearing young sporophyte, with a single sporangium and adventitious roots!
It reproduced like the vegetable cryptogams, especially the Pteridophyta, having spore cases at the tips of the wings and evidently developing from a thallus or prothallus.