Observations on mitochondrial growth are recorded from the meristem of a liverwort(Anthoceros laevis) and from a Chrysophycean flagellate (Chrysochromulina brevifilum). No sign of de novo origin has been obtained in either case. In both the commonest form of mitochondrial reproduction is from growth leading to clusters of mutually attached mitochondria which are presumed to separate later. Some stages in the formation of clusters are illustrated and some of the processes involved analysed in a preliminary way. Mitochondrial growth is seen to be a somewhat more complicated total process than has sometimes been thought.