4 ON GENERA AND SPECIES. 



stances of observation and discrimination, uncertainty often 

 prevails. For instance, no class of plants has of late 

 years been more written about than the Ferns of Great 

 Britain ; and yet much diversity of opinion still exists 

 amongst British botanists regarding the number of species, 

 although they have the opportunity of carefully and 

 leisurely examining them under every circumstance con- 

 nected with the different aspects they assume in their 

 various places of growth. This surely offers some pallia- 

 tion for the errors committed by the general pteridologist, 

 more especially when we consider that the Ferns of Great 

 Britain are in number as one to sixty of the Fern-flora of 

 the earth. 



Having had under my observation for nearly half a cen- 

 tury the Fern collection in the Royal Gardens at Kew, 

 which, as already stated, amounted in 1864 to about a 

 thousand species, and having during that period carefully 

 noted their different modes of growth and aspects, I have 

 been induced to consider that the differences seen in a series 

 of closely allied living Ferns, are much more obvious than 

 in examples of the same when seen in the herbarium. It 

 is, however, often difficult to express their differences in 

 words, but the eye readily distinguishes them, and knowing 

 that each form maintains its own peculiar habit from year 

 to year, reproducing its like from spores (seeds), I am, 

 therefore, induced to consider that although closely allied, 

 they are nevetheless sufficiently different to be regarded as 

 distinct species. 



Another point which renders it difficult to arrive at 

 any satisfactory conclusion as to the correct number of 

 species, is the botanical rule which prescribes that the 

 specific name under which a plant is first described, is to 

 be retained in whatever genus it may be referred to by 



