The chalaza is a structure inside bird and reptile egg

Egg (biology)

An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...

s and plant ovule

Ovule

Ovule means "small egg". In seed plants, the ovule is the structure that gives rise to and contains the female reproductive cells. It consists of three parts: The integument forming its outer layer, the nucellus , and the megaspore-derived female gametophyte in its center...

s. It attaches or suspends the yolk or nucellus within the larger structure.

In animals

In the eggs of most birds and 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. For culinary use of eggs, particularly 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 micropyle

Micropyle

A micropyle is small opening in the surface of an ovule, through which the pollen tube penetrates, often visible as a small pore in the ripe seed....

 opening of the integuments. It is the tissue where the integuments and nucellus are joined. Nutrients from the plant travel through vascular tissue in the funiculus

Funiculus

The cerebrospinal fibers consist of numerous nerve fibers collected together and enclosed in membranous sheaths. A small bundle of fibers, enclosed in a tubular sheath, is called a funiculus; if the nerve is of small size, it may consist only of a single funiculus; but if large, the funiculi are...

 and outer integument through the chalaza into the nucellus. During the development of the embryo sac inside a flowering plant

Flowering plant

The flowering plants , also known as Angiospermae or Magnoliophyta, are the most diverse group of land plants. Angiosperms are seed-producing plants like the gymnosperms and can be distinguished from the gymnosperms by a series of synapomorphies...

 ovule, the three cells at the chalazal end become the antipodal cells.

Chalazogamy

In most flowering plants, the pollen tube

Pollen tube

The pollen tubes is the male gametophyte of seed plants that acts as a conduit to transport the male sperm cells from the pollen grain, either from the stigma to the ovules at the base of the pistil, or directly through ovule tissue in some gymnosperms .After pollination, the pollen tube...

 enters the ovule through the micropyle

Micropyle

A micropyle is small opening in the surface of an ovule, through which the pollen tube penetrates, often visible as a small pore in the ripe seed....

 opening in the integuments for fertilization (porogamy). In chalazogamous fertilization, the pollen tube

Pollen tube

The pollen tubes is the male gametophyte of seed plants that acts as a conduit to transport the male sperm cells from the pollen grain, either from the stigma to the ovules at the base of the pistil, or directly through ovule tissue in some gymnosperms .After pollination, the pollen tube...

s penetrate the ovule through the chalaza rather than the micropyle opening.
Chalazogamy was first discovered in monoecious plant species of the Casuarinaceae

Casuarinaceae

Casuarinaceae is a family of dicotyledonous flowering plants placed in the order Fagales, consisting of 3 or 4 genera and approximately 70 species of trees and shrubs native to the Old World tropics , Australia, and the Pacific Islands...

 family, but has since then also been observed in others, for example in pistachio

Pistachio

The pistachio, Pistacia vera in the Anacardiaceae family, is a small tree originally from Persia , which now can also be found in regions of Syria, Lebanon, Turkey, Greece, Kyrgyzstan, Turkmenistan, India, Pakistan, Egypt, Sicily and possibly Afghanistan , as well as in the United States,...

 and walnut

Walnut

Juglans is a plant genus of the family Juglandaceae, the seeds of which are known as walnuts. They are deciduous trees, 10–40 meters tall , with pinnate leaves 200–900 millimetres long , with 5–25 leaflets; the shoots have chambered pith, a character shared with the wingnuts , but not the hickories...

.