The thesis is presented in two parts. PART I. A study of Cucurbitaria piceae Borthwick, a disease of the buds of the Spruce. PART II. A study of Pseudopeziza ribis Kleb. (Gloeosporiura ribis (Lib.) Mont. and Desm.), the Leaf Spot disease of the black currant. The work which forms the basis for Part I was carried out at the Department of Botany of the University of Edinburgh prior to September 1952. It was continued, under leave of absence, together with the work described in Part II, at the Department of Agriculture and Horticulture of the University of Bristol.