My Chianti Rose tomato seedlings have been transplanted into small pots. You can tell it is time when roots start poking out of the peat puck and once the first set of true leaves come in. I learned a new term. Those first set of fat leaves that appear upon germination are called cotyledons, which are the embryonic leaves or seed leaves.
The number of cotyledons present is one characteristic used by botanists to classify the flowering plants (angiosperms).
Species with one cotyledon are called monocotyledonous (or, “monocots”) and placed in the Class Liliopsida.
Plants with two embryonic leaves are termed dicotyledonous (“dicots”) and placed in the Class Magnoliopsida.