 Overall, the 4th edition was a mild expansion of the 3rd, from 18 to 20 volumes, and was updated in its historical, scientific, and biographical articles.Some of the long articles were entirely re-written for the 4th edition.For example, the 56-page "Botany" of the 3rd edition was replaced in the 4th with a 270-page version by moving all the individual plant articles into one.