78 
THE FERN FORESTS OF 
naked, like the stem of the Cactus. Beside 
these, there are the tree-like Equiseta, in which 
we find the articulations on the trunk correspond- 
ing exactly to those now so characteristic of 
those marsh-grasses which are the modern repre- 
sentatives of this family of plants, with cone-like 
fructifications on the summit of the stem. 
I would merely touch here upon a subject 
which does not belong to my own branch of Nat- 
ural History, but is of the - greatest interest in 
botanical research, namely, the gradation of 
plants in the geological ages, and the combina- 
tion of characters in some of the earlier vege- 
table forms, corresponding to that already no- 
ticed in the ancient animal types. For instance, 
in the Carboniferous period we have only Cryp- 
togams, Ferns, Lycopodiacese, and Equisetaccse. 
In the middle geological ages, Coniferae are intro- 
duced, the first flowering plant known on earth, 
but in which the flower and fruit are very imper- 
fect as compared with those of the higher groups. 
The Coniferae were chiefly represented in the 
middle periods by the Cycadse, that peculiar 
group of Coniferae, resembling Pines in their 
structure, but recalling the Ferns by their exter- 
nal appearance. The stem is round and short, 
its surface being covered with scars similar to 
those of the Ferns ; while on the summit are ten 
or more leaves, fan-like and spreading when their 
