Genetic engineering and cell and tissue culture have already begun to influence the breeding and vegetative propagation of superior rootstocks and woody perennial trees for efficient forestry systems and urban plantings. In our laboratory, hard-to-root biomass species such as Douglas-fir, white sprace, and jack pine have been cloned through micropropagation. The American elm has been propagated from cell suspension cultures. With similar methods being used for fruit and nut trees, valuable root-stocks of Prunus and Pistacia species are at the point of being cloned and modified to capture the maximum genetic variation available. Currently, a considerably smaller proportion is obtained through conventional selection and breeding.