by Nathaniel Lord Britton & Addison Brown, An Illustrated Flora of the Northern United States… (1913)
“ Pollen-grains (microspores) dividing at maturity into two or more cells, one of which gives rise to the pollen-tube (male prothallium) , which directly fertilizes an archegone of the nutritive endosperm (female prothallium) in the ovule. ”
