Difference Between Hilum and Micropyle

Main Difference – Hilum vs Micropyle

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.

This article explores,

1. What is Hilum
– Definition, Structure, Role, Characteristics
2. What is Micropyle
– Definition, Structure, Role, Characteristics
3. What is the difference between Hilum and Micropyle

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 1.

Figure 1: Hilum of black-eyed peas

What is Micropyle

The micropyle is the small opening in the integuments of the ovule which enable the sperms to access the ovum during fertilization. In angiosperms, sperms are carried by the pollen tube. In gymnosperms, sperms are carried on a drop of fluid. The chalaza is found in the opposite side of the micropyle. Before germination, embryo absorbs water through the micropyle. During germination, radicle emerges through the micropyle. Radicle is the part of the embryo plant which develops into the primary root. In monocot seeds like costar seeds, the micropyle is totally covered by the caruncle. The absorbing water by the caruncle percolates through the micropyle into the seed. Structure of the dicotyledon seed is shown in figure 2.

Figure 2: Dicotyledon seed structure

Definition

Hilum: Hilum is the elliptical scar found on the seed, marking a point of attachment of the funicle.

Micropyle: Micropyle is the small opening in the integuments of the ovule which enable the sperms to access the ovum during fertilization.

In Monocot Seeds

Hilum: Hilum is partially covered by the caruncle.

Micropyle: Micropyle is totally covered by the caruncle.

Role

Hilum: Hilum is the point which attaches the ovule to the placenta.

Micropyle: Water is absorbed through the micropyle into the embryo during germination of the seed.

Conclusion

Hilum and micropyle are two markers found on the seed coat. The ovule attaches to the placenta via funicle. After fertilization, ovule develops to the seed. The attaching point of the funicle to the ovule is the hilum. Micropyle is another mark found on the seed coat. It is the small opening found in the integuments which surrounds the embryo sac. Pollen tube enters the ovule through the micropyle. During germination, water is absorbed into the embryo through the micropyle. The main difference between hilum and micropyle is their function of each structure.

Reference:
1.”Seeds and their Morphological Features (With Diagram).” Biology Discussion. N.p., 27 Aug. 2015. Web. 09 May 2017. <http://www.biologydiscussion.com/plants/seeds-and-their-morphological-features-with-diagram/6334>.

Image Courtesy:
1. “BlackEyedPeas” By Toby Hudson – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Dycotyledon seed diagram-en” By LadyofHats – Own work. Image renamed from File:Dycotyledon seed diagram.svg (Public Domain) via Commons Wikimedia