The germination requirements of Fraxinus excelsior, the European ash, were determined as a preliminary stage to an investigation of the growth-substance content of dormant and germinating fruits. The embryo grows in size within the imbibed fruit before germination can take place and this growth is delayed through the first winter by the presence of an indehiscent pericarp which is impermeable to oxygen. Even when fully grown, the embryo is dormant and completes its chilling requirement during the second winter, after which a normal seedling can be produced.