AS COMPARED WITH THAT OF THE PRESENT DAY. 399 



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 of 

 other orders; as is thus shown. 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 Diemen's Land and New Zealand, 

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

 the one hand, and admitting no under-growth of smaller species on 

 the other. 2. A luxuriant vegetation of many species of ferns, con- 

 tinued 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 vegetations 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 total 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 Sand- 

 wich 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 

 climate of the carboniferous period being temperate, equable and 

 humid ; and so it no doubt 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. If, however, the laws of existing vegetation are to be con- 

 sidered as having had equal force at that time when the fossil one 



* This preponderance of ferns over flowering plants is common to many tropical islands, 

 and not confined to the smaller of them, as St. Helena and the Society group. In extra- 

 tropical islands, too, as New Zealand, I have collected as many as 36 kinds of fern in an 

 area not exceeding a few acres : they gave a most luxuriant aspect to the vegetation, which 

 presented scarcely a dozen flowering plants and trees besides. An equal area in the 

 neighbourhood of Sydney (in about the same latitude) would have yielded upwards of 100 

 flowering plants and but two or three ferns. 



