Ancient Vegetation of the Earth, 323 
the earth was subjected during this period? The operations of 
nature now going on in different regions of the globe, may throw 
some light upon this question. 
The study of the geographical distribution of those plants ap- 
pertaining to the same families which alone composed the vege- 
tation of the coal period, may, indeed, indicate to us the climac- 
terick conditions and consequently the physical causes which 
favoured the increase of stature as well as the great frequency of 
these vegetables ; and we may conclude from these, with much 
probability, that the same causes determined their preponderance 
at that epoch. 
We see, for example, that the Ferns, Equiseta, and Lycopodize 
attain a more lofty stature in proportion as their geographical po- 
sition approaches the equator. Thus it is only in the hottest 
‘regions of the globe that we find those arborescent Ferns which 
combine with the towering and majestick mien of the Palms, the 
elegant foliage of the ordinary Ferns, and of which we have 
indicated the existence in the coal formations. In these same 
regions the Equiseta and Lycopodiz attain to a stature double or 
triple that which the largest of these species present in temperate 
climates. A second condition appears to have a still more marked 
influence upon their preponderance, in reference to the vegetables 
of other families, namely, humidity and uniformity of climate ; 
conditions which are united in the highest perfection, in ibe small 
islands situated far distant from continents. 
In such islands, indeed, the extent of the surrounding oceans 
fixes a temperature with but slight variations, and coupled with 
tual humidity ; circumstances which appear to favour, in a 
remarkable manner, the development and the variety of specifick 
forms among the Ferns and the analogous plants; while, on the 
contrary, under the influence of the same conditions, the pheno- 
gamous plants are little varied, and are far less numerous. From 
these causes it results, that while on the extensive continents of 
the earth the vascular Cryptogamick plants, such as the Ferns, 
Lycopodize, Equiseta, &c. often form scarcely one fiftieth of the 
total number of vegetables, yet in the small islands of the equa- — 
torial regions, these same plants constitute almost half, and in 
some cases, even two thirds of all the vegetables which inhabit 
them. 
