PREFACE. 
vn 
a sorus or heap, and usually consists of many membranous 
capsules, thecae or sporangia , with or without an elastic ring. 
The ring is designed to aid, both in the bursting of the capsule, 
and in the dispersion of its contents. If a frond of the com- 
mon Hartstongue be gathered on an open day in winter, and 
the under surface be suddenly exposed to the sun, and the 
result observed with a magnifier, this phenomenon of the 
dispersion of the spores, or seed-buds, may be seen to great 
advantage. The sori, or bundles of capsules, are sometimes 
elevated upon a flat or saucer-shaped receptacle ; and some- 
times arranged round a stalk : rarely, the capsules lie soli- 
tarily, or in pairs, upon the frond itself. The sori, again, 
may be observed to be covered with a membrane, called an 
indusium, or involucre, or they are naked. From these cha- 
racters, and from the form, arrangement, absence, or presence 
of them, Ferns are divided into tribes, genera, and species. 
Species are the distinct kinds belonging to one genus ; genera 
are the distinct forms belonging to one tribe. And species 
may be further divided into varieties ; as the Hartstongue, 
Scolopendrium vulgare, has no less than sixty-five marked 
variations from the simple or normal form, catalogued by 
cultivators of the species.* 
Collectors of Ferns, whose knowledge of the primary charac- 
ters of a species has been confined to the study of a few fronds, 
perhaps of one only, upon a limited locality, are often tempted 
to assume unusual deviations from the primary characters, as 
proofs of a distinct species : and by this means, the names of 
Ferns have been greatly and inconveniently multiplied. There 
is no necessity to give a name to every variety of form : the 
* See Vol. y. pp. 156, 157, Ferns Brit, and Exotic, by E. J. Lowe. 
