they have in our less productive region. The actual amount of 

 species, indeed, almost constantly diminishes with the increase of 

 latitude beyond the tropics. 



In a work intended as an aid to the less scientific observers and 

 admirers of natural productions, it is not considered desirable to 

 enter into those minutiae of organic composition, by which the 

 physiologist is guided in his studies of the relative structures and 

 affinities of the various groups composing the vegetable kingdom ; 

 but, as certain general characters appertain to that before us, and as, 

 in describing families and species, it is convenient to employ a few 

 conventional terms, expressive of features and conditions not be- 

 longing to other plants, a concise view of the peculiarities by 

 which ferns are collectively distinguished, becomes a necessary in- 

 troduction to their examination in detail. 



With much of the aspect belonging to the higher orders of vege- 

 tation, and occasionally rivaling in port and habit the more ma- 

 jestic of their forms, ferns have a structure indicative of a much 

 lower grade in organization, and may be regarded as occupying an 

 intermediate position, or rather as representing the most compli- 

 cated type of that class characterized by the absence of flowers. 

 They are, with slight exception, perennial plants, but vary much in 

 habit, and especially in the development of the stem ; this is gene- 

 rally either procumbent or it extends itself below the surface of the 

 soil, and from its root-like appearance is denominated a rhizoma, 

 though some writers designate it as the caudex. Rarely, and almost 

 exclusively in very warm and humid climates, ferns are arborescent 

 the stem growing erect like the trunk of a tree, when it is called 

 the stipes, and in some species attaining a height of forty or fifty 

 feet : it is cylindrical, of equal diameter throughout, and bears 

 leaves only at the summit, like a palm, the necessary result of its 

 growth being only from the termination of the axis. Occasionally 

 a tendency to upright elongation of the rhizoma is observed in 

 some of the larger species of the British Ferns. The leaves, usually 



