The chalaza (; ; : chalazas or chalazae ) is a structure inside and plant . It attaches or suspends the yolk or nucellus within the larger structure.
In animals
In the eggs of most birds (though not in eggs of reptiles
), the chalazae are two spiral bands of tissue that suspend the yolk in the center of the white (the albumen). The function of the chalazae is to hold the yolk in place. In baking, the chalazae are sometimes removed in order to ensure a uniform texture.
In plants
In plant ovules, the chalaza is located opposite the
Ovule opening of the integuments. It is the tissue where the
and
nucellus are joined. Nutrients from the plant travel through vascular tissue in the
Ovule and outer integument through the chalaza into the nucellus. During the development of the embryo sac inside a
flowering plant ovule, the three cells at the chalazal end become the antipodal cells.
Chalazogamy
In most flowering plants, the
pollen tube enters the ovule through the
Ovule opening in the integuments for fertilization (porogamy). In chalazogamous fertilization, the
penetrate the ovule through the chalaza rather than the micropyle opening.
Chalazogamy was first discovered in
monoecious plant species of the family
Casuarinaceae by
Melchior Treub, but has since then also been observed in others, for example in
pistachio and
walnut.
Notes
