274. 'Eating the plant of the field', or fodder that is wild, is to live like a wild animal. This is clear in Daniel in reference to Nebuchadnezzar,

They will drive you away from human beings, and your dwelling will be with the beast of the field; you will be made to eat the plants like oxen; and seven times will pass over you. Daniel 4:32.

And in Isaiah,

Have you not heard that I did it long ago and planned it from days of old? Now I have brought it to pass, and it will be that strongholds, fortified cities, will be devastated into heaps; and their inhabitants, shorn of power', were dismayed and filled with shame; they became plants of the field and edible plants, grass on rooftops, and scorched earth before standing corn. Isaiah 37:26-27.

This makes explicit what 'plants of the field' means, and what 'edible plants, grass on rooftops, and scorched earth' means, for the subject here is the time before the Flood, which is what 'long ago' and 'days of old' are used to mean.