Cotyledons

The first set of leaves that appear on a seedling are called Cotyledon. Cotyledons are formed during embryo-genesis, along with the root and shoot meristems, and are present in the seed prior to germination. True leaves, however, are formed post-embryonically (after germination) from the shoot apical meristem, which is responsible for generating subsequent aerial portions of the plant. Meristem is the tissue where cells divide and growth takes place.
Cilantro is displaying it's true leaves now and each plant is approximately 3 to 3.5 inches tall.

Basil is much slower in growth. Although it is only about an inch tall, it is displaying its true leaves.

The nasturtiums seem very hardy. At 6 inches tall, they are dominating the growth race. The cotyledons have grown very aggressively and look almost identical to it's true leaves. I was forced to move the light fixture up 3 inches to accommodate the growth. In a few days I will be pinching the top to force a more compact growth habit.