a structure within which a plant embryo develops; spec. (in an angiosperm) a thin-walled sac inside the nucellus of the ovule within which…

Botany and Mycology. The larger of the two types of spore produced by a heterosporous plant (now usually called megaspore); (also) the larger of…

The larger of the two kinds of spores produced by heterosporous cryptogams, which develops into the female gametophyte. Also: the analogous…