1. The scar on the seed coat comprising a corky abscission layer where the seed or ovule was attached to the funiculus. In some -species it may be large and highly coloured and may be used as a diagnostic character.
2. A point in a starch grain around which layers of carbohydrate are deposited. It can be detected when starch grains are stained with dilute iodine solution. The position of the hilum may be characteristic of a species. If the layering is uniform, the hilum is in the centre of the grain (e.g. maize starch) but if it is uneven, the hilum may be to one side (e.g. potato starch). In some cases (e.g. rice starch) there may be more than one hilum in each grain.