Due both to ease of production and handling as well as the potential for specialized treatment, seed is the preferred vehicle for the propagation and cultivation of most agronomic and forest tree species (Gray, 1990). However, a glance at the list of the world’s top crops (Witt, 1985) reveals that 10 of the 30 crops with an annual production of between 10 and 450 million metric tonnes are vegetatively propagated. For a variety of reasons, including genetic self-incompatibility, uniformly homogeneous seed can either not be produced or utilized for a number of agronomical and horticultural crops (Redenbaugh, 1990a,b). In these cases, plants are propagated vegetatively, such as sugarcane and fruit crops, or by genetically non-uniform seed, as for example lucerne (alfalfa) and forage grasses.