CHAPTER XIV. 



FERNS, FERN ALLIES, AND FOSSILS. 



In past geological periods, Ferns were the dominant 

 vegetation, and were very widely distributed ; but 

 now they never occupy large areas, and, though 

 common in subordinate positions, they are of little 

 importance. In Scotland there are often great 

 stretches of Bracken on the lowland sheep farms, 

 which seem at first to be a special association of 

 plants in which the fern retains something of its old 

 supremacy ; but this Bracken formation is generally 

 found on parts of the country which were in all prob- 

 ability formerly covered either by light oak scrub, or by 

 pine and birch ; and, probably, it represents woodlands 

 from which the trees have been removed. The limits 

 of altitude to which the bracken extends are very 

 nearly the same as those of the Pine. 



On the whole. Ferns and their allies are decidedly 

 a decaying family, driven from the best situations by 

 better developed forms. In Britain they generally 

 occur in the deep shade of well-grown trees, and in a 

 moist atmosphere, though there are several exceptions. 

 The little Wallrue {Asplenium ruta-mwaria), and some- 

 times Maidenhair Spleenwort (^Aspleniuin trichomanes), 

 flourish on the stones of bridges and walls, where they 

 are much exposed to drought. Ceterach officuiarum is 

 also a hardy fern, able to exist in very dry situations. 



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