Abstract: In angiosperms, two sperms have been recognized as cells linked together by themselves and closely associated with the vegetative nucleus in pollen grain or in pollen tube ;o form so called the “male germ unit (MGU)”In addition to MGU, recent studies have shown the existence in several plants that the two sperm cells in pair may be very different in size, shape, organelle content, and sperm heteromorphism. The concept of the MGU and sperm heteromorphism has appeared in more than 40 reports and has triggered new research concerning the angiosperm fertilization process, In this review, a survey and analysis of the MGU and sperm heteromorphism in literature of last decade are presented and the new experimental approaches are suggested.

Key words: Male germ unit, Sperm heteromorphism, Three-dimensional reconstructions, Quantitative cytology