Fig. 3. Spherical and cylindrical structures in 0.20 µm thick sections of wild-type S. cerevisiae cells grown at 37°C. (a) A poorly perforated sheet of endoplasmic reticulum curves (ER) and forms a cylindrical structure (white arrow). A large, well-stained vacuole (V) is located adjacent to the nucleus (N). Magnification x38,500. (b) Three vacuole-like spherical structures (V) are connected to the nuclear envelope (N). The vacuole structure at the top-right is continuous with a sheet of unperforated ER (ER). A tubular network (arrow) is also labeled. Magnification x52,400. (c) Connected to the nuclear envelope, an unperforated ER sheet (ER) forms cylindrical structures (arrows). N, nucleus. Magnification x67,400.