Fig. 1. Three stereopairs of 0.20 µm thick sections of wild-type S. cerevisiae cells grown at 24°C. (a) Shows a nucleus (N) delimited by a lightly stained nuclear envelope in continuity with ER sheets or ribbons seen in side view (ER). One of these ER elements is continuous (arrow) with a strongly stained tubular network, probably a Golgi element (G). Another sheet of ER seen in face view (er) is in close proximity to another strongly stained tubular network showing more intensely stained nodular dilations (G). Intensely stained free secretion granules (SG) are interspersed throughout the cytoplasm. CW, cell wall. Magnification x18,800. (b) Lightly stained ER ribbons are seen in oblique or side views (ER). Strongly stained structures resembling secretion granules (white arrow) are observed at the left-hand extremity of an obliquely sectioned ER ribbon. Spherical membranous structures (V) resembling vacuoles are in close contact with the nuclear envelope. N, nucleus. Magnification x40,500. (c) A non-perforated ER sheet (ER) seen in face view is continuous at its periphery with lightly stained anastomosed tubules (arrows) forming a wide-meshed tubular network. At the right-hand side extremity of this network, there are more intensely stained dilations (arrowheads) that resemble secretion granules (SG). Magnification x74,000.