ORGANOGRAPHY. 
47 
Fully developed fronds vary in size from less than an inch to 15 
or 20 feet in length, and from a line, or even less, to 10 or 15 fee 4 " 
in breadth. They also vary in form, in circumscription, and in 
texture ; aud they are either furnished with a leaf-stalk ( stipes ) 
or are leafy to the base (sessile). 
In describing the form, circumscription, texture, and surface of 
the fronds of Ferns, the same terms are employed as in the case of 
the leaves of flowering plants. They vary from simple entire to 
decompound-multifid. In compound fronds the primary divisions 
are termed pinna, and when more than once divided, the ultimate 
ones pinnules ; and the terms applied to simple fronds are equally 
applicable to these divisions. The divisions or branches of their 
stipes also are termed the rachis. 
Their texture is very different in different species. Some being 
thin, membranous, and even pellucid, while others are thick and 
coriaceous, or fleshy, rigid or flaccid. 
The surfaces of the fronds are either quite smooth, or furnished 
with different kinds of hairs, glands, or scales (the latter have 
received the name of ramenta, and are generally membranorfs and 
deciduous), or they are covered, particularly the under surface, 
with white or yellow farina. 
The plants called Fern Allies differ entirely in habit and mode 
of growth from true Ferns ; that the word fronds is not applicable ; 
but as the genus Selaginella is called “ fem-like plants,” I there- 
fore apply the term “ frondules” to the species with distinct stems, 
and to the main branches of the surculose species. 
VEINS. 
In Ferns the mode in which the veins are disposed in the sub- 
stance of the fronds, or the venation, as it is termed, is of more 
importance than in flowering plants, the characters relied upon for 
distinguishing the genera depending more or less upon it, and 
there are numerous terms applied to it. 
The midrib of simple fronds, or of the pinnae or pinnules of 
compound fronds, is called the costa, and is in the former a con- 
tinuation of the stipes, gradually decreasing in thickness towards 
the apex, or altogether disappearing (evanescent), and in the latter 
