Why can't red beans grow into anything other than red bean plants?

Nagashree was talking to me about Classification of Plants and animals yesterday. The following question came up: If you look at two varieties of bean plants (say red bean and brown bean) just when they sprout, they look similar. But when they grow up they produce different varieties of beans. The red bean variety always produces red bean plants and the brown ones always produce brown bean plants. What is in the bean seed that determines what the plant grows into ? And what is the process involved?

Nagashree, try to find more on the above question.

A related question: Certain lizards re-grow their tails when their tails are cut off. Why does that not happen to most other animals?