Description (From Recipaedia)
Plant Rye on tilled, moist and fertilized soil to obtain full grown plants. Harvesting the plants will yield large number of rye seeds. Rye also grows naturally in form or wild rye. You can obtain wild seeds by harvesting it.
Growing Rye
Rye is the cultivated version of Wild Rye. Properly planting and growing wild rye seeds will give you the cultivated rye plants. The plants mature in several stages and you must wait until they are fully grown. You need the seeds from harvesting the cultivated rye, to make flour for your bread. This block is only obtainable within Creative mode or glitches.