THE 



FERNS OF GREAT BRITAIN. 



INTRODUCTION. 



FERNS constitute a series of vegetable productions of consider- 

 able extent, amounting to upwards of two thousand known species, 

 the greater proportion of which is found in tropical climates, but 

 very unequally distributed; the general habit of the fern leading it 

 to develop most freely under the joint influence of shelter from the 

 sun and wind, and an atmosphere replete with moisture. Hence 

 the open prairie, the pampa, and the steppe offer conditions most 

 unfavourable to their growth ; while the land covered with dense 

 forests, or the mountain with its rocky clefts and caverns, affords 

 the requirements upon which it depends, especially where such 

 occur in association with a warm and vaporous climate. The pro- 

 portion that ferns bear to the aggregate vegetation of different 

 countries, though in some measure dependent upon such circum- 

 stances, conveys no definite idea of their real numbers : thus, when 

 we learn that in the British Islands they compose ^ y th of the con- 

 spicuous vegetation of the land, and in tropical America ^th, we 

 are not to conclude that the numbers in the two countries at all 

 approximate, but that amidst the exuberant development of the 

 torrid zone the ferns maintain an equal proportion to that which 



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