The archegonium is a female sexual organ found in plants, particularly within the bryophytes. This female reproductive structure is typically a single cell made up of a venter and a long neck which both contain special tissues and cells. On the upper part of the venter is a pore known as the micropyle, which helps the entrance of sperm from the male antheridia. The archegonium contains a gametophyte, which is a haploid cell that helps produce an egg after fertilization by a sperm. The egg can then develop into a new sporophyte individual.
The walls of the archegonium are made up of four to five layers, with the first being the innermost layer which is closest to the egg cell. This layer is specially adapted so that sperm may enter the egg cell. Subsequent layers form a protective coat against the environment, and are hydrophilic in nature, allowing the transfer of water and nutrients across the layers.
In contrast to the male antheridia, the archegonium has a slower reaction time and maturation time. It may take days or weeks for the archegonium to form, and it may take days or months for it to mature enough to accept and fertilize the sperm. Furthermore, after the sperm enters the archegonium, it takes some time for the egg to develop and for an embryo to form. Thus, the archegonium’s role in reproduction is vitally important, but it is also incredibly slow and inefficient in comparison to the male antheridia.