The morphology of mitochondria extracted from beet (Beta vulgaris L.) tissue was examined by phase contrast and electron microscopy and compared with the structure of mitochondria in tissue sections. The structure of the beet mitochondria proved much more labile than that of animal mitochondria and no really satisfactory way of preserving it was found. However, it was demonstrated that the organelles, which were either spherical or ovoid, were bounded by typical double membranes, presumably lipo-protein, about 170 Å thick. Internally the mitochondria contained membraneous structures embedded in a finely granular matrix.