The part labelled I is called the cotyledons. In many plants, the cotyledons are the first leaves to emerge from the seed and can even become photosynthetic, especially in epigeal germination (where the cotyledons emerge above ground). 

Cotyledons, often called "seed leaves," are embryonic leaves within a seed that store nutrients and provide initial nourishment for the developing seedling, especially before it can photosynthesize. It contains stored food reserves (like starch, fats, and proteins) that are essential for the seedling's early growth and development.