4/9 Except in a few places where brackets are used to indicate passages previously published. In all such cases the meaning of the symbol is explained.) Dots indicate omissions, but many omissions are made without being so indicated. Our plan has been to classify the letters according to subject--into such as deal with Evolution, Geographical Distribution, Botany, etc., and in each group to place the letters chronologically. But in several of the chapters we have adopted sectional headings, which we believe will be a help to the reader. |