The protoplasm in the mycelium and conidiophores of the barley mildew (Erysiphe graminis DC.) is continuous from cell to cell. Each transverse septum is provided with a minute central pore through which passes a delicate strand of cytoplasm 1–1.5 μ in width. The cytoplasmic strands and the septal pores have been readily demonstrated by means of a slight modification of Wahrlich's technique, and their presence recorded by means of photomicrographs and drawings. The cytoplasmic connections have also been seen in living unstained mycelium.Streaming of cytoplasm from cell to cell was not observed in the present study, possibly because of the slow rate of flow or because of the difficulty of examining the mycelium without disturbing it.