From Dan Levitt, Cambridge, Massachusetts, US
Thanks to Guy Cox for noting that, 100 years ago, chloroplasts were known to be structures in cells. In my article, I was referring to the state of knowledge in the 1920s and 30s about human cells. Outside the nucleus, the only structures known then were mitochondria, whose function was unknown, and putative Golgi bodies, believed to be artefacts of the cell-staining process (Letters, 26 August).
