stock

1. (rootstock) A plant onto which shoots or buds (scions) of another plant are grafted. The stock affects the size, vigour, and time of flowering and fruiting, of the scion, and specially bred rootstocks are selected accordingly. Where necessary rootstocks may be chosen that confer frost hardiness or resistance to certain soil-borne pathogens. See grafting.
2. A maintained culture of a particular organism, the origins and characteristics of which are known.