In such places, by a variety of means, plants are now flourishing on the earth which represent practically all the main stages of development of plant life as a whole. It is to the study of the simpler of the living forms that we owe most of our conceptions of the course taken by evolution. Had we to depend on fossil evidence alone, we should be in almost complete ignorance of the earliest types of vegetation and all the simpler cohorts of plants, because their minute size and very delicate structure have always rendered them unsuitable for preservation in stone. At the same time, had we none of the knowledge of the numerous fossil forms which we now possess, there would be great gaps in the series which no study of living forms could supply. It is only by a study and comparison of both living and fossil plants of all kinds and from beds of all ages that we can get any true conception of the whole scheme of plant life. Grouping together all the main families of plants at present known to us to exist or to have existed, we get the following series:— Group. Common examples of typical families in the group. Thallophyta Algæ Seaweeds. Fungi Moulds and toadstools. Bryophyta Hepaticæ Liverworts. Musci Mosses. Pteridophyta Equisetales Horsetails. Sphenophyllales* fossil only, _Sphenophyllum_. Lycopodales Club-moss. Filicales Bracken fern. Pteridospermæ Lyginodendræ* fossil only, _Sphenopteris_. Gymnosperms Cycadales Cycads. Bennettitales* fossil only, _Bennettites_. Ginkgoales Maidenhair Tree. Cordaitales* fossil only, _Cordaites_. Coniferales Pine, Yew. Gnetales Welwitschia. Angiosperms Monocotyledons Lily, Palm, Grass. Dicotyledons Rose, Oak, Daisy. In this table the different groups have not a strictly equivalent scientific value, but each of those in the second column represents a large and well-defined series of primary importance, whose members could not possibly be included along with any of the other groups. Those marked with an asterisk are known only as fossils, and it will be seen that of the seventeen groups, so many as four are known only in the fossil state. This indicates, however, but a part of their importance, for in nearly every other group are many families or genera which are only known as fossils, though there are living representatives of the group as a whole.