All Flesh Is Grass

by Clifford D. Simak

For this was the day about which there had been speculation—although far too little speculation and too little done about it because it seemed so distant and so improbable. This was the day that the human race had come into contact (or perhaps, collision) with an alien race. All the speculation, of course, had concerned an alien out of space, an alien on, or from, some other world in space. But here was the alien, not out of space, but time, or at least from behind a barrier in time.

even if we could, should we keep them out? Even in the face of potential danger, should we bar the way to them? For here was an alien life, the first alien life we’d met. Here was the chance for the human race, if it would take the chance, to gain new knowledge, to find new attitudes, to fill in the gaps of knowing and to span the bridge of thought, to understand a non-human viewpoint, to sample new emotion, to face new motivation,

all the animal life on Earth, including man, depended on the plants of Earth for their energy.