To solve this problem, we need to identify the term used for the cotyledon of a maize grain.$\newline$Let's analyze the options:$\newline \bullet$Plumule: This is the part of a seed embryo that develops into the shoot, bearing the first true leaves. It is not the cotyledon.$\newline \bullet$Coleorhiza: This is a sheath protecting the root of a germinating grass seedling. It is not related to the cotyledon.$\newline \bullet$Coleoptile: This is a protective sheath covering the emerging shoot in monocotyledons like maize. It is not the cotyledon.$\newline \bullet$Scutellum: This is the term used for the single cotyledon in monocotyledons such as maize. It is a specialized structure that absorbs nutrients from the endosperm during germination.$\newline$Therefore, the cotyledon of a maize grain is called the scutellum.$\newline$The correct option is Option 4: Scutellum.