Webster’s Revised Unabridged Dictionary · 1913
Prothallus
Pro·thal′lus (·lŭs), n.; pl. Prothalli (#). [NL., fr. Gr. πρό before + θαλλός a young shoot.] (Bot.) The minute primary growth from the spore of ferns and other Pteridophyta, which bears the true sexual organs; the oöphoric generation of ferns, etc.