A seed has a small pore outside it,from where air and light enter to keep it alive.It is called micropyle and the point where the seed is attached to its stalk,is called hilum.
Both hilum and micropyle are two characteristic markers found on the seed coat. Seed coat is developed from integuments which surround the embryo sac. It consists of a multi-layered tissue, including a hard, protective, mechanical layer. This layer is covered by a water-impermeable cuticle. Hence, seed coat prevents the destruction of the seed by predation or dehydration. The third marker on the seed coat is raphe, a ridge adjacent to the hilum, which occurs due to the fusion of the funicle to the side of the ovule. The main difference between hilum and micropyle is that hilum is an elliptical scar on the seed, which marks the point of attachment of the funicle whereas micropyle is the small end of the hilum in which the pollen tube go through prior to fertilization.
What is Hilum
The hilum is the elliptical scar found on the seed, marking a point of attachment of the funicle. Funicle is the filamentous stalk that attaches the ovule to the placenta. In beans, hilum is called the “eye”. Another elliptical scar is found in the middle of the seed coat and is called chalaza or strophiole. A distinct ridge called raphe runs from hilum to chalaza. Raphe is caused by the fusion of the funicle to the side of the ovule. In costar seeds which are monocots, hilum is partially covered by the caruncle, which is the white, spongy, bi-lobed outgrowth. Caruncle is present near the narrow end of the monocot seed. Hilum of the black-eyed peas is shown in figure