This is an image assembling of a epicotyl embedded in a sprouting bean. It is manually assembled using photoshop. (30% overlaping is needed for software automatical assembling.) The leaf has grown to the similar size of the bean but is still embedded in the bean. Although it has the morphology similar to a leaf, it is still called epicotyl rather than leaf. Only when it  splits cotyledons and struggles out shall it be called firstleaf. This is why firstleaves are always one and only one pair. The small graph on the left shows the epicotyl in a unsprouting seed, which is the precursor to the large sprouting epicotyl (and thus firstleaves).

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