INTRODUCTION. 43. 
while the Polypodiacee include the greater portion of all known 
Ferns. These three groups may each be regarded as a distinct 
order of plants, forming together the Frrices or Ferns. 
The groups thus indieated are distinguished from each other by 
the nature and structure of their spore-cases. The presence of the 
annulus or ring around the spore-case, in some form or other, either 
nearly completely surrounding it, or in a more or less rudimentary 
condition, is the distinctive peculiarity of the Polypodiacee, while 
the Marattiacee and the Ophioglossacee, are distinguished by the 
absence of any such ring, rudimentary or otherwise. These obvious 
distinctions, to which, as they are connected with certain other 
differences which serve the same purpose, the initiated seldom have 
to resort, are the foundation of all satisfactory inquiries into the 
nomenclature of a Fern. 
The Marattiacee and Ophioglossacee are distinguished from each 
other by very obvious characters. The Marattiacee are dorsiferous, 
that is, bearing their sori on the back or under surface of their 
fronds, as is commonly the case among Ferns. The Ophioglossacee, 
on the contrary, always have their spore-bearing or fertile fronds 
contracted, so that while the spore-cases are produced marginally, 
they seem to occupy the whole surface; such fronds are called 
rachiform, because they want the flat leafy expansion of ordinary 
fronds, and are reduced to the appearance of mere ribs or rachides. 
The Ophioglossacee are few in number, and present little differ- 
ence of structure, so that it has not been found necessary to range 
the genera in secondary groups or tribes. The Marattiacee, however, 
form three little groups of genera, separated by differences of some 
importance; these tribes are called the Marattinee, the Kaulfussinec, 
and the Daneinee. The Marattinee have their sori ranged in two 
lines facing each other, forming distinct oblong masses. The Kaul- 
Jussinee have distinct circular sori, the spore-cases of each sorus 
being concrete into a single annular series, and furnished with 

