Practice question

Annulus consists of specialized row of thick-walled hygroscopic cells with inner and radial walls heavily thickened with lignin in U-shaped pattern, forming arc partially encircling leptosporangium capsule on one side. Upon dehydration under low humidity, annulus cells lose water, contract differentially, storing elastic energy, then snap backward violently rupturing stomium region and ejecting spores catapult-like up to several centimeters into air stream. Nutrition or protection functions performed by tapetum and indusium, germination unrelated process. Presence and position provide taxonomic characters distinguishing fern families.