Fragments from the Lost Writings of Irenaeus, XXXI

Observe that, by means of the grain of mustard seed in the parable, the heavenly doctrine is denoted which is sown like seed in the world, as in a field, [seed] which has an inherent force, fiery and powerful. For the Judge of the whole world is thus proclaimed, who, having been hidden in the heart of the earth in a tomb for three days, and having become a great tree, has stretched forth His branches to the ends of the earth. Sprouting out from Him, the twelve apostles, having become fair and fruitful boughs, were made a shelter for the nations as for the fowls of heaven, under which boughs, all having taken refuge, as birds flocking to a nest, have been made partakers of that wholesome and celestial food which is derived from them.