The egg apparatus of N. tabacum was studied from just before flower opening until 92 h after pollination. Each synergid has a large nucleus and nucleolus and a prominent chalazal vacuole. Numerous mitochondria, plastids with starch, dictyosomes, free ribosomes and rough endoplasmic reticulum (ER) are present. A cell wall exists only around the micropylar half of the synergids and each cell has a distinct filiform apparatus. Numerous conspicuous cell-wall evaginations located just chalazal to the hook region extend laterally from the synergids into the central cell. The egg has a chalazally located nucleus with a single nucleolus and a large micropylar vacuole. With the exception of dictyosomes, the same cytoplasmic organelles are present in the egg as in the synergids, but in much lesser amounts. A continuous cell wall is not present around the chalazal end of the egg. Before pollination, numerous large lipid bodies are localized in the outer integumentary cells. Near the time of fertilization many large starch grains are found within the central cell, and following fertilization there is a buildup of starch grains in the integument with a concomitant reduction of lipids in the integument and starch in the central cell. After pollination but before the pollen tube reaches the ovule, 1 of the 2 synergids begins to degenerate. It is consistently this synergid which receives the pollen-tube tip and its discharge. Polysaccharide-containing vesicles of pollen-tube origin were observed fusing with the cell walls of the pollen tube, the degenerate synergid and the persistent synergid. Little change in the zygote cytoplasm was noted. The zygote is about 27% smaller than the egg. A complete cell wall forms around the chalazal end of the zygote, presumably by an involvement of the ER cisternae, since no dictyosomes were observed in the zygote.