72 ON GENERA AND SPECIES. 



ciated with a host of species ditFering- widely in habit. 

 Admitting' that a greater or lesser number of species 

 possess some character in common to entitle them to be 

 called genera, nevertheless, genera may be said to have no 

 real existence in nature, but, by adopting them, we are 

 enabled to study and classify Ferns so as to convey to the 

 mind our ideas regarding the various forms and nature of 

 the numerous plants that come under our observation. 



In the preceding observations I have shown that habit 

 is of great importance as a character for determining the 

 relationship of Perns to one another, cither as individual 

 species or groups of species, but habit is not always avail- 

 able, especially in describing from herbarium specimens 

 alone, for it is only the small growing kinds, with caudex 

 and fronds united, that are suited for the herbarium. A 

 great number consists of single fronds, or even portions of 

 fronds, only, consequently, the nature of their vernation is 

 unknown. Indeed, the great botanists of the present day 

 content themselves with describing plants from dried spe- 

 cimens, many of which are often small and imperfect, and 

 fail to convey the true nature of the plant in its living 

 state. 



The celebrated botanist ilr. Bcntbam says: — "I have 

 published several thousands of new species of plants, I 

 have never published one without examining it in a her- 

 barium, and I have examined very few in botanical 

 gardens." This practice I cull unfortunate, for although 

 the living collection at Kow may not at any time exceed 

 one-tenth of the species in the herbarium collection, never- 

 theless it affords ample materials for verifying and assisting 

 to correct errors in many descriptions made from herbarium 

 specimens only. With regard to the collection of living 

 Ferns, which the author of the " Species Filicum " calls 



