The studies by John Ray in the 1700's on the structure of seeds led him to discover the difference between monocotyledon (monocots) and dicotyledon (dicots) plants. There are estimated to be about 165,000 different types of dicots and 55,000 types of monocots.

Monocots have only one cotyledon, dicots have two cotyledons. A cotyledon contains stored food and serves as a food reservoir. Aside from the difference between the seeds of monocots and dicots there are other different structures that separate monocots and dicots. Monocots have long, narrow leaves with parallel veins (such as grasses.) The parts of monocot flowers are arranged in threes or in multiples of three. Dicots have broad leaves with branched veins. The parts of dicot flowers are arranged in fours and fives or multiples of fours and fives. Although the distinction between monocots and dicots is not always as sharp and clear as once thought, it is a useful taxonomic grouping.