'Grain' in the Bible

It is like to a grain of mustard, which a man having taken, did cast into his garden, and it increased, and came to a great tree, and the fowls of the heavens did rest in its branches.'

and the Lord said, 'If ye had faith as a grain of mustard, ye would have said to this sycamine, Be uprooted, and be planted in the sea, and it would have obeyed you.