OX GENERA AND SPECIES. 5 



subsequent authors ; and in consequence of many species 

 of Linnaeus, Swartz, and other early authors, being but 

 indifferently described, many being- founded on imperfect 

 specimens, and nothing but the meagre description left us 

 for their identification. It frequently happens that some 

 modern author detects or supposes that he has found out 

 that the new species of his contemporary is one of the 

 Linnean or Swartzian doubtful species, and on his decision 

 being confirmed, names long familiar have to be changed. 

 Again, by the distribution of trade and private herbarium 

 collections, sets of the same specimens fall in the hands of 

 different botanists at the same time, and each being eager 

 to describe what he considers new, and not, in some in- 

 stances, having studied the special families, nevertheless 

 does not hesitate to describe new species, or to found new 

 genera. This being done without inter-communication, 

 different names are given to the same plants ; when these 

 are collated by the systematist, it often becomes difficult to 

 decide which to adopt, thus burdening the science with 

 synonyms. 



Under this state of things few Ferns have now less than 

 three names, many have twenty, thus rendering it in many 

 cases impossible to reconcile one author's views with an- 

 other's. For instance, the Fern known by the name of 

 Ceratopteris thalictroides has been described by no less than 

 twelve authors under as many different generic and specific 

 names. 



But the point upon which pteridologists appear to 

 differ most, and upon which their only agreement seems to 

 be an agreement to differ, is the definition of genera and 

 their limits. I say emphatically appear to differ, for in the 

 works of those most at issue the differences are not so 

 much in the limits of the groups themselves as in the 



