have successively occupied the surface of the Earth. 81 



in Europe comprehend about 250 different species, and the 

 whole of Europe now only produces 50 species. 



In the same way, the Gymnospermia, which now only com- 

 prise in Europe about 25 species of Coniferse and Ephedrea, then 

 contained more than 120 species of very different forms. 



These families, existing alone and much more numerous then 

 than they are now in the same climates, if we embrace the entire 

 carboniferous period, were still more remarkable for the very 

 different forms under which they presented themselves; thus 

 among the Cryptogamia we observe genera of Ferns now com- 

 pletely destroyed, and several arborescent species ; the Equiseta 

 or allied plants almost arborescent ; the Lycopodiacese forming 

 gigantic trees ; all forms now unknown, either in the entire world 

 or at least in the temperate zones. 



Among the plants that we range with the Gymnospermous 

 Dicotyledons, the differences are still more striking, for they 

 constitute families completely extirpated since that epoch ; such 

 are the Sigillariese, the Noeggerathiese, and the Asterophyllitese. 



The characters of the vegetation during the carboniferous 

 period may be thus summed up : — 



Complete absence of Angiospermous Dicotyledons ; 



Complete or almost complete absence of Monocotyledons ; 



Predominance of Acrogenous Cryptogamia and forms unusual 

 and now destroyed in the families of the Filices, Lycopodiacese 

 and Equisetacese ; 



Great development of the Gymnospermous Dicotyledons, but 

 resulting from the existence of families completely destroyed, not 

 only now but from the close of that period. 



Must we suppose that this vegetation, thus reduced to forms 

 which we are led to consider as 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 ? This we are 

 unable to decide. 



1 will merely recall to mind, that 1 have already noted the 

 analogy this predominance of Acrogenous Cryptogamia esta- 

 blishes between the vegetation of this first period and that of 

 the small islands of the equatorial and southern temperate zones, 

 in which the maritime climate exists in the fullest condition. 



At the same time this predominance is not such that it in- 

 volves, as during the carboniferous period, the exclusion of Pha- 

 nerogamous plants ; and that complete exclusion would seem more 

 favourable to the idea of a gradual development of the vegetable 

 kingdom. 



