'Grain' in the Bible

It happened that he was going on the Sabbath day through the grain fields, and his disciples began, as they went, to pluck the ears of grain.

For the earth bears fruit: first the blade, then the ear, then the full grain in the ear.

It's like a grain of mustard seed, which, when it is sown in the earth, though it is less than all the seeds that are on the earth,