Corn plants are 2 blocks high, and yield corn cobs. These can be
cooked to corn-on-the-cob, or processed to make corn seed (corn
kernels, basically).
Digging a mature plant yields the corn cob. A harvested corn plant
"wilts", and needs to be dug away to make the land usable, or can
be left as ornamental 2-block plant. Digging either top or bottom
block works in all cases, although I need to verify that I've
covered every block combo.
This should be entirely working now - MELONS!
Work as expected. A seed grows to a plant, plant flowers and an
adjacent melon block grows, and is attached with a stem. Once the
melon block is harvested (which drops 3-5 melon slices), the
stem is lost and the plant will grow a new melon from it's mature
stage.