JW^il 
I 
3 
THE FORMS OF ANCIENT VEGETATION. 
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developed — not merely specific differences, more frequently profound differences, so that new genera or 
families take the place of genera and families destroyed and completely extinct. A more general and 
important result also presents itself, namely, the predominance in the most ancient times of acrogenous 
eryptogamic plants (Ferns and Lyeopods) ; later, the predominance of gymnosperrnous dicotyledons 
(Cycads and Conifers) -without the admixture yet of a single angiospcrmous dicotyledon ; finally, 
dining the cretaceous formation, the appearance and soon the predominance of angiospcrmous plants, 
both dicotyledons and monocotyledons. We may divide the long series of ages which have presided 
over this successive birth of the different forms of the Vegetable Kingdom, into three long periods — 1, 
the reign of the Acrogens ; 2, that of the Gymnospernis, and 3, that of the Angiosperms. 
I. The great predominance of the acrogenous division, and in particular of the families of Ferns and 
Lyeopodiacese, the considerable number of species of the first of these families, the great development 
of the plants of the second, and the arborescent, form of the Lepidodendron. form the most striking 
characters of this reign, which comprises the Carboniferous and Peruvian periods. The long carboni- 
ferous period begins with the appearance of the first terrestrial vegetables deposited in certain layers 
of the transition formations, and extends to the new red sandstone which covers the coal formation. 
The characters of the vegetation ma}" be summed up thus : — The complete absence of angiospcrmous 
dicotyledons ; the complete absence (or nearly so) of monocotyledons; the predominance of acrogenous 
cryptogams, and forms unusual aud now destroyed in the families of Ferns, several arborescent 
Lyeopods forming gigantic trees, and Equisetums almost arborescent ; the great development of 
gymnospermous dicotyledons of families completely destroyed from the close of that period Must we 
consider that this vegetation, thus nearly reduced to forms which we consider the most simple and 
least perfect, owed that special nature to its being a first phase of the development of the organization 
of the vegetable kingdom, which had not yet attained to the perfection it subsequently arrived at; or 
was it due to an influence of the physical conditions in which the surface of the earth was then placed ? 
We arc not sufficiently acquainted with the influence of the nature of the atmosphere upon the life of 
vegetables, when prolonged through their entire existence, to know whether important differences in 
the composition of that atmosphere, and, above all, the (very probable) presence of a greater proportion 
of carbonic acid might not favour the existence of certain classes of the vegetable kingdom, and oppose 
that of other groups. The nature of the plants which appear peculiar to the Permian period is far 
from being positively determined. 
II. During the preceding period, the acrogenous cryptogams predominate, and the gymnospermous 
dicotyledons, less numerous, present themselves in forms unusual and sometimes anomalous. Subse- 
quently these anomalous and ambiguous forms disappear. The Ferns and Equisctacese arc less 
numerous. The Cordferae and Cycadacea? almost equal them in number, and ordinarily surpass them in 
frequency ; and by their abundance and dimensions become characteristic. Angiospcrmous dicotyledons 
are still wholly wanting, and monocotyledons are very few in number. This second kingdom is 
divisible into two periods. 1. The Vosgcsiau period, which docs not appear to have had long duration, 
presents the following characters :— the existence of a tolerable number of Ferns of forms frequently 
anomalous, manifestly constituting genera now destroyed; the stems of arborescent Ferns more 
frequent than in the next period ; true Equiseta very rare ; Calamitcs, or perhaps rather the Calamo- 
dendra, abundant ; gymnosperms represented by two Coniferous genera, the species and specimens of 
which arc numerous, while Cycadacea? are very rare. 2. The Jurassic period, one of the most 
extensive in regard to the formations it comprises, aud the variety of special epochs of vegetation 
embraced in it, comprising from (lie Keuper inclusively to the Wcaldcn formations. In this period 
the Cycadacea' become predominant by the number of species, their frequency, and the variety of the 
generic forms. The flora of the Keupric epoch resembles that of the lias in the Ferns, aud some forms 
of Cycads. The Liassic epoch is distinguished by the great predominance of Cycadacea-, and the 
existence among the Ferns of many genera with reticulated nervation. The Oolitic epoch, compre- 
hending from tiie lias up to the "Wcaldcn formation exclusively, is characterized by the rarity of the 
Ferns with reticulated nervation, numerous in the lias, and the frequency of genera of the Cycadacea 
most analogous to those now existing. In the Wcaldcn epoch the generic forms are almost all the 
same as those of the lias and oolitic formations; nevertheless, the Cycadacea' already appear less 
numerous in proportion to the Ferns. This fresh-water formation, which terminates lor us the 
kingdom of the Gymnosperms, is allied by its total character to other epochs of the vegetation of the 
Jurassic period; and is distinguished from the cretaceous epoch, which succeeds it. by the complete 
absence of every species which can lie referred to the angiospcrmous dicotyledona 
III. The predominant character of this transformation of the vegetation of the globe is the appear- 
ance of the angiospcrmous dicotyledons; of those plants which at the present time constitute nunc than 
