132 Scientific Intelligence. 



under growth of a limited number of kinds of fern,* for a very limited 

 number of them (comparatively speaking), if as protean as some of 

 their allies are in our day, would embrace all the known species of the 

 Fossil Flora. 



In the temperate latitudes particularly, a recent Flora marked by a 

 preponderance of ferns, is almost universally deficient in species or 

 other orders ; as is thus shewn. 1. Where one species prevails over 

 a considerable area, as the bracken (Pteris aquilina) does in parts of 

 Britain, and the P. esculenta in Van Diemens Land and New Zealand, 

 it generally monopolizes the soil, choking plants of a larger growth on 

 the one hand, and admitting no undergrowth of smaller species on the 

 other, 2. A luxuriant vegetation of many species of ferns, continued 

 through a great many degrees of latitude or longitude, especially in 

 the temperate regions of the globe, generally indicates a uniformity of 

 temperature throughout that area, and a paucity of species of flower- 

 ing plants. A comparison of the vegetation of Tasmania and New 

 Zealand illustrates this. The former of these islands, barely 200 

 miles long, contains four times as many species of flowering plants as 

 New Zealand, whose tolal length is 900 miles. On the other hand, 

 this latter country possesses more than four times as many kinds of 

 fern as Tasmania, and they are so uniformly distributed over its area, 

 that almost all those which are found at the southern extremity of the 

 island, prevail also at the northern. The West Indian and Pacific 

 Islands again present a flora, remarkably rich in ferns, and, in both 

 these instances, we have very many of the species uniformly spread 

 over an enormous surface, in the one instance, from the windward 

 Islands to Mexico ; and, in the other, from New Zealand to the Society 

 and Sandwich Islands. Take, on the other hand, the campos of Brazil, 

 the sandy flats of Southern Africa, and the somewhat similar plains of 

 Australia, and sterile though they appear at first sight, they will be found 

 to abound in many kinds of flowering plants; but unaccompanied with 

 ferns. 



This prevalence of ferns has been long adduced in proof of the cli- 

 mate of the carboniferous period being temperate, equable, and humid; 

 and so, no doubt, it was ; but I am not aware that it has been hitherto 

 regarded as probable evidence of the paucity of other plants, and the 

 general poverty of the whole flora which characterized that formation. 

 lt\ however, the laws of existing vegetation are to be considered as hav- 

 ing had equal force at that time when the fossil one flourished, we must 

 conclude that the predominance of ferns in general, and of certain 

 species of Pecopteris (a fern apparently allied to our Pteris), over a 

 great area, together with the remarkable similarity of the English fos- 

 sils with those of North America, are all indications that the flora of 

 that period was poor in number of species. 



* This preponderance of ferns over flowering plants Is common to many tropical 



islands, and not confined to the smaller of them, M St. Helena and the Society group. 

 In extratropical islands, too, as New Zealand, I have collected as many as thirty-six 



kinds of fern in an area not. ew.pp.r liner a few acres : thev c*avp a most luxuriant as- 







An 



flowering plants, and but two or three ferns 



