Fig Mitochondria in phloem parenchyma cells of a maize leaf. Magnification bar = 1 m m. Mitochondria in living cells are highly pleomorphic, as shown by phase contrast microcinematography by Hongladarom et al., (1965). Pleomorphism is reflected also in thin section electron microscopy, in which mitochondria appear as roughly circular profiles as well as highly elongated or irregular cross sections (Fig. 5.1a). The circular sections may represent transverse or oblique sections through an otherwise elongated organelle. The diameter of the elongated mitochondrion appears to be about 0.4 to 0.5 µm, while the length may be several micrometers long. Although rods or apparent spheres are the most common profiles seen, sections derived from branched or cup shaped organelles have also been discerned (Bagshaw et al., 1964). The recent analysis of serial sections of yeast cells by Hoffman and Avers (1973), which showed that yeast contains a single, giant, branched mitochondrion, suggests that the irregular cross sections of mitochondria of other cells might also be sections of a single branched organelle. From .