THE ULTRASTRUCTURE AND COMPOSITION OF THE EGG AND CENTRAL CELL OF COTTON

The ultrastructure and composition of the egg and central cell of Gossypium hirsutum (cotton) was investigated. The egg is a large, highly vacuolate cell partially surrounded by a wall. This wall, which is thickest at the micropylar end of the cell, disappears approximately 2/3 of the length of the cell from the micropylar end. The chalazal 1/3 of the cell is surrounded by a plasma membrane. The egg cell shows many characteristics, both in structure and composition, of an inactive cell. No indication of the destruction or formation of cell organelles was found in the egg during the period covered in this study. The central cell is a large, highly vacuolate cell and contains the two polar nuclei. A description of the fusion of the polar nuclei through membrane fusion is given. The nuclear membranes of the polar nuclei are apparently highly active. Indeed, the entire central cell appears active. Much of this activity may be associated with the enlargement of the central cell and the breakdown of the nucellus. The differences in the metabolic condition between the egg and central cell at the time of double fertilization may influence the subsequent initial rate of development of the zygote and the endosperm.