Slide showing a diagram from a book regarding comparative physiology of yellow stock and green stock. Slide shows a diagram from a book regarding comparative physiology of yellow stock and green stock. The writing above the diagram reads: 'Comparative Physiology / from the parental yellow since it is capable of giving / rise to green offspring: it differs presumably in'. The diagram shows combinations resulting from Pure Yellow Stock and Pure Green stock. Small white label in the upper left corner of slide reads: 'Newton & Co, 43 Museum St, London, W.C.1.' Newton & Co were manufacturers of lantern slides and had various branches in London. Late 19th to early 20th century