This LM and the following EM illustrate the principle that mitochondria size and location is indicative of the function of the cell. HA31 is cardiac muscle stained with iron hematoxylin to emphasize the striations (A bands (dark) and I bands (light)). It shows the mitochondria (m) at either end (pole) of the nucleus. This cell, which requires ATP for continuous contraction, has very large mitochondria. Their central location is optimal to allow the maximum space for contractile proteins.