Oliver was a professional botanist. Originally from
Oliver and John Ruskin knew each other through their mutual interest in plant life. Like Ruskin, Oliver thought that botany was an interesting and useful subject for young people to learn about. He himself had introduced a new classification of plant life by the age of 20, at 21 had become a fellow of the Edinburgh Botanical Society, and at 23 a Fellow of the Linnean Society. In 1864 he published Lessons in Elementary Biology, which ran into several editions over 30 years and was promoted as a textbook for young people working away from school. Oliver was talented enough as an artist to illustrate his books himself.