The term “clone” is a key biological term that designates a number of horticultural situations. In breeding, many cultivars are designated as clones, originating from consecutive vegetative propagation from individuals within a seedling population, from individual plants of a clone exhibiting “bud mutations,” and, more recently, from genetic engineering and biotechnology. Extensive vegetative propagation of a limited numbers of clones in modern horticultural systems has been accompanied by systemic incorporation by serious pathogens (viruses, viroids, phytoplasmas, etc.), and in some cases by horticultural deterioration (e.g., noninfectious bud-failure in almonds). Control of these problems in clonal propagation is achieved by 1) propagation source selection 2) maintenance of the source in a registered foundation block under protected conditions and 3)multipli-cation in controlled “mother blocks” or “increase blocks” from which commercial material is distributed after a minimum of consecutive generations of vegetative propagation. This system is the basis for Registration and Certification programs and “clean stock” in general. In many crops the selected propagation source is a single plant, its progeny constitutes a “clone,” and the new entity is given a unique name or number. To distinguish this “new” clone from the “original” clone, the designation of FOUNDATION CLONE is suggested. Biological and horticultural significance is illustrated in almond (Prunus dulcis).