4 
BRITISH FERNS, 
whose age is indicated by concentric rings of growth, 
and also most flowering plants. 
2nd. Endogens, or such as increase their stems by 
the deposit of fresh substance from within. This group 
includes many trees, as the palms, and flowers, as the 
lily tribe and grasses. 
3rd. Acrogens, or such as increase by a deposit from 
the base of the leaves or fronds at the summit. This 
includes the ferns and mosses. And 
4th. Thallogens, or such as increase by an outspread 
membrane, or thallus. This includes the lichens, alg^e, 
and fungi. 
Acrogens are either vascular and fern-like, or cellular 
and moss-like. Ferns may be described scientifically as 
“ plants of vascular structure which produce fruit with- 
out preliminary flowers.” 
In their affinities, ferns are connected the most closely 
with flowering plants through the Cycad group. In this 
group, the vascular system is developed in much the 
same degree as in the ferns; the leaves are pinnate like 
the fronds of ferns, and are rolled in youth in the style 
which in ferns is called the vernation. The cycads have 
naked ovules bordering their contracted leaves, so as to 
create a further resemblance between such leaves and 
the altered fronds of the Osmunda and Lunaria. 
Another system of dividing is into two classes — Phae- 
nogams, or flowering-plants, and Cryptogams, or flower- 
less plants. Ferns rank as the highest order of crypto- 
gams. They are a very numerous family, and of very 
ancient descent. The genera now known are 192 in 
number, and contain 2040 species. Some of these, as 
the Norfolk Island Tree-fern, attain a stature of twenty 
feet ; while others, as our Filmy-ferns, are scarcely an 
inch in height. 
