The seeds contain endosperm and a straight embryo with two oval-elliptical or circular cotyledons. The cotyledons are usually unequal in size, and the endosperm is minimally present. Cabbage seedlings have a thin taproot and cordate (heart-shaped) cotyledons. The shoot apical meristem is between the cotyledons. Some secondary cell walls store nutrients, such as those in the cotyledons and the endosperm. The "apical embryo domain", gives rise to the shoot apical meristem and cotyledons. Germination is hypogeal and cotyledons remain within the seed coat. Epigeal germination implies that the cotyledons are pushed above ground. On the maternal side, these villous tree structures are grouped into lobules called cotyledons. Hypogeal germination implies that the cotyledons stay below the ground. In addition, oblong embryos continued axial growth, without the introduction of cotyledons. Dicot seedlings grown in the light develop short hypocotyls and open cotyledons exposing the epicotyl. The seedlings of some flowering plants have no cotyledons at all. The embryo can be straight or curved, and has two cotyledons. The seedlings have three to nine, but usually six, cotyledons each.