main lines of evidence. The most convincing' is that gained from 
fossils, or the remains or imprints of plants or animals of the 
past. The fossil evidence relating- to the horse has been called 
the “ edition de luxe" of evolution, because every link is found 
between the modern horse and its five-toed ancestor. 
But in most cases the fossil links are incomplete, and it 
becomes necessary to complete the tree of evolution by evidences 
from the comparison of living forms (morphology) , and by their 
development (ontogeny) . Thus, the fact that frogs come from 
tadpoles suggests their ancestors, the fishes. The thread-like 
protonema , the early stage of mosses, suggests their ancestors, the 
algae. The prothallium , the early stage of a fern, is very much 
like a liverwort. 
In House No. 2 of the conservatories of the Brooklyn Botanic 
Garden, types of the principal groups of plants have been arranged 
to indicate their approximate relationships, that is, in the form of 
a tree. The trunk denotes the main course of plant evolution ; on 
the branches, representatives of the various groups are growing. 
The label for this exhibit is reproduced on page 2. On the left 
are data showing important steps which have led toward a natural 
classification of plants; and on the right, a diagram, intended to 
represent approximately present views as to plant evolution. These 
groups are assigned somewhat varying ranks by different botanists. 
It is not proposed here to outline a complete plant classification. 
Important stages of plant evolution may be summarized as follows : 
1. Algae, mostly water plants, without archegonia. Fungi 
are a side line. 
2. Liverworts and Mosses, moist-soil plants, with archegonia, 
but no roots. 
3. Clubmosses and Horsetails, “dry” land plants, with 
roots. Leaves small. 
4. Ferns, leaves large , no seeds. 
5. Cycads and Ginkgo, naked seeds, sperms swimming. 
ti. Conifers, naked seeds, sperms not swimming . 
7. Dicotyledons and Monocotyledons, seeds enclosed in a 
fruit. 
These various groups may be described more in detail as 
follows : 
1. Algae. The blue-green algae and green algae live chiefly 
in fresh water and include the simplest forms. The bacteria are a 
distinct and probably very ancient group. Slime molds exhibit 
characters of both plants and animals. The brown and the red 
algae or seaweeds grow chiefly in salt water. 
The fungi seem to represent several distinct side lines of de- 
velopment, characterized by absence of chlorophyll. Land forms 
such as lichen* are doubtless very ancient, mushrooms compara- 
tively recent. All these plants are called Thallophytes ; they have 
no true leaves. 
2. In the liverwort* and moiie*, life on moist land became 
possible by the development of small bottle-shaped structures 
