Electron micrographs of root hair cells of Azolla imbricata show in the vacuoles a number of heavily electron-dense bodies. They appear to be aggregates of particles of ca 30 m[mu] in diameter and are probably of lipid nature. The mitochondria are typical of plant cells. Plastids in cells treated with osmium fixatives appear to contain lamellae and grana-like structures. Cells fixed with permanganate plastids show grana-like structures, but there are no stroma lamellae. The endoplasmic reticulum appears in the shape of discrete layers or in stacks of lamellar layers. Palade granule-like bodies are seen in osmium-fixed cells, but not in permanganate-fixed cells. The Golgi-like structures are composed of cisternae. Small discrete vesicles are often found at the edges of the cisternae. These vesicles appear more clearly in permanganate-fixed cells than in osmium-fixed ones.