The development of hybride has vastly increased yields and other desired characteristics of a number of important crops. Basically, hybrids are offspring of crosses between two different true-breeding strains. Often quite different from either parent strain, hybrids tend to exhibit "hybrid vigor" and to have significantly higher yield. The most success with hybrid crops has been obtained with corn(maize). Corn is one of the easiest plants to hybridize because of the physical separation of the maile flower, which grow as tassels on top of the corn plant, from female flowers, which are attached to incipient ears on the side of the plant. Despite past successes by more conventional means and some early disappointments with "genetic engineering," application of recombinant DNA technology (Section 16.13) will probably eventually overshadow all the advances ever made in plant breeding.