128 HOW TO KNOW THE FERNS 



no attention from the passers-by. Of course, cer- 

 tain species of Fern are extremely local, largely 

 owing to the fact that they require special con- 

 ditions of soil, etc. It is therefore quite useless 

 to look for such in an average district. Many 

 species flourish only in rock crevices or on old 

 walls. Others are to be found, as a rule, in 

 rather elevated positions, and we cannot hope 

 to find them save in a mountainous country. 

 Finally, there are a great many Ferns which can 

 adapt themselves to a variety of conditions. 

 The actual circumstances of their surroundings 

 will make them vary more or less from the 

 type, and this must always be borne in mind 

 when specimens are being examined. In another 

 way identification is sometimes rather difficult, 

 owing to the fact that immature Ferns are often 

 very misleading in their appearance. Quite 

 likely they may resemble another species al- 

 together. It is therefore only when a mature 

 frond bearing sporangia is discovered that it is 

 possible in some cases to speak with certainty. 

 Many British Ferns evidence a marked ten- 

 dency to " sport," and this is a fact which the 

 beginner should always bear in mind. As a 

 rule, however, even in the case of extreme 

 varieties, a careful examination of the specimen 

 will enable it to be identified. 



