The inflorescence of the monoecious maize plant is unique among the Gramineae in the sharp separation of the male and female structures. The male tassel at the terminus of the plant most often sheds pollen before the visual appearance of the receptive silks of th the female ear at a lateral bud, normally at the 10 leaf [I]. Earlier studies examined the ontogeny of the growing tissues beginning with the embryo in the kernel through to the obvious protuberances of the growing point as the kernel germinates. The differentiated developing soon-to-become tassel and the lateral bulges that develop into the ears on the lateral buds become apparent very early in the germinating kernel [2, 3, 46]. A certain number of cells are destined for tassel and ear development [8]. As the plant develops, there is a phase transition [\3, 16] from the vegetative lateral buds to the reproductive lateral buds. This change in phase has been ascribed to genotypic control as evidenced in the differences among different genotypes in the initiation of the reproductive [I]. The genetic control of tassel and ear initiation has been gleaned from anatomical observations. Lejeune and Bernier [I2] found that maize plants terminate the initiation of additional axillary meristems at the time of tassel initiation. This would indicate that the top-most ear shoot is initiated on the same day as the initiation of tassel development and this event signals the end of the undifferentiated growing point.

The inflorescence of the monoecious maize plant is unique among the Gramineae in the sharp separation of the male and female structures. The male tassel at the terminus of the plant most often sheds pollen before the visual appearance of the receptive silks of th the female ear at a lateral bud, normally at the 10 leaf [I]. Earlier studies examined the ontogeny of the growing tissues beginning with the embryo in the kernel through to the obvious protuberances of the growing point as the kernel germinates. The differentiated developing soon-to-become tassel and the lateral bulges that develop into the ears on the lateral buds become apparent very early in the germinating kernel [2, 3, 46]. A certain number of cells are destined for tassel and ear development [8]. As the plant develops, there is a phase transition [\3, 16] from the vegetative lateral buds to the reproductive lateral buds. This change in phase has been ascribed to genotypic control as evidenced in the differences among different genotypes in the initiation of the reproductive [I]. The genetic control of tassel and ear initiation has been gleaned from anatomical observations. Lejeune and Bernier [I2] found that maize plants terminate the initiation of additional axillary meristems at the time of tassel initiation. This would indicate that the top-most ear shoot is initiated on the same day as the initiation of tassel development and this event signals the end of the undifferentiated growing point.

The International Symposium on "Cellular and Molecular Aspects of Biosynthesis and Action of the Plant Hormone Ethylenc" ,vas held in Agen, France from August 31 st and September 4th, 1992. The planning and management of the scientific and social programme of the Conference were carried out jointly by the "Ethylene Research Group" of ENSAlIN"P (Toulouse) and Agropole Congres Service (Agen). Since the last meetings in Israel (1984) and in Belgium (1988), ethylene physiology has gone through a period of exciting progress due to new developments in cellular and molecular bioiogy. New methods and tools have been developed to better understand the role and functions of ethylene in fruit ripening, flower senescence, abscission, piant growth, and cell differentiation. Genes involved in ethylene biosynthesis have been characterized and transgenic plants with altered ethylene production have been generated. The feasibility of delaying fruit ripening or flower senescence by genetic manipulation is now demonstrated, thus opening new perspectives for the postharvest handling of plant products. Some progress has also been made on the understanding of ethylene action. However, much remains to be done in this area to elucidate the ethylene signal transduction pathway. Around 140 scientists from 20 countries attended the Symposium. They presented 47 oral reports and 40 poster demonstrations. All of them are published in these proceedings. It has been a pleasure for us to organize this important Symposium and to edit this book.