scattered about in the form of fine dust. In Osmunda, Botrychium, and Ophioglossum, the spore-cases have not the elastic ring, but are composed of two valves.

In the greater part of the British species, the sori are covered during the earlier period of their growth with a thin membranous covering, which is called an indusium. Some ferns possess this organ, which is very evident when they are young. It is, however, cast off as the sori attain maturity. The presence or absence of this indusium is looked upon as an important point in the economy of ferns, and they are divided according to this fact.

Although the spore is often called the representative of the seed, this little structureless body truly represents the bud in higher plants. If we watch the development of the spore, we shall find that it does not directly grow up into a fern, but that, after having attached itself to a damp piece of earth or rock, it begins to expand into the form of a green membrane This green membranous mass, on account of its resemblance to the fronds of the common Marchantia, has been called the Marchantia-like expansion of the fern. It is also called the prothallus. On the surface of this little body, there appear in the course of time two sets of organs. The one called pistillidia, containing in their interior little ovoid bodies, which are the representatives of the ovules or seed-buds of the higher plants. The other organs are called archegonia they contain little movable worm-like bodies, called spermatazoids, and which are found in many of the lower forms of plants. These bodies represent the pollen or pollen-tube of the flowering plants. They find their way to the ovules contained in the pistillidia; and it is after the mixture of the produce of these two different cells that the young fern shoots forth from the surface of the prothallus, and grows up into a new plant.

ON THE CLASSIFICATION OF FERNS.

In the account of British ferns given in this little work, they have been arranged alphabetically; but in order that the student may have an idea of their general structure, we present an analysis of the characters of the orders and genera into which they are divided by botanists. It must always be remembered, that the species of British ferns are only a small part of the great family of ferns which are scattered in space over the surface of the earth, and in time in the rocks of which the earth is composed. No arrangement of fragmentary groups, such as the British ferns, can give the student an idea of the grandeur, beauty, and harmony of the whole. But the study of this limited portion of the great family will, it is hoped, kindle in him a desire to know more of this great family, which, though deprived by their Creator of the beauty and adornment of flowers, have nevertheless attractions and graces of their own, and, with all other created things, the charm of occupying a necessary place in the great order of creation.

ARRANGEMENT OF THE GENERA OF BRITISH FERNS.

POLYPODIACEÆ.

The fronds are rolled up in a circinate manner while young, the spore-cases have an elastic ring, which bursts by an irregular transverse cleft.

I. POLYPODIACEÆ.

Sori round, without an indusium.

1. POLYPODIUM.-The sori dorsal, circular, and exposed.

2. ALLOSORUS.-Sori dorsal, roundish, and becoming confluent beneath the margins of the frond.

II. GYMNOGRAMMEÆ.

Sori linear, without an indusium.

3. GYMNOGRAMMA. Sori dorsal, linear, forked, naked.

III. ASPIDIEÆ.

Sori covered with a circular or roundish indusium, springing from the back of the veins.

4. ASPIDIUM.-Sori dorsal, with circular, peltate, or reniform indusia.

IV. ASPLENIEÆ.

Sori covered with an oblong or elongated indusium, which springs from the sides of the veins.

5. ASPLENIUM.-Sori dorsal, with a straight and elongated indusium.

6. SCOLOPENDRIUM.-Sori dorsal, elongate, and placed together in parallel pairs, the indusium opening along the centre.

7. CETERACH.-Sori dorsal, hidden amongst rustcoloured chaffy scales; the indusium invisible.

V. BLECHNEÆ.

The sori with an indusium forming longitudinal lines between the midrib and margins of the pinnæ. 8. BLECHNUM.-Sori dorsal, covered by a linear indusium.

VI. PTERIDEÆ.

Bearing on the margins of fronds, sori, which are covered with a special indusium.

PTERIS.—Sori in a continuous line at the edge of the

frond.

VII. ADIANTEÆ.

The margins of the fronds reflexed, forming indusia, which bear the sori beneath.

9. ADIANTUM.-Sori dorsal, in patches, covered with a reflexed indusium.

VIII. CYSTOPTERIDEÆ.

Sori with special ovate indusia attached behind, and inflected hood-like over them.

10. CYSTOPTERIS.—Sori dorsal, with a cucullate or hood-like indusium.

IX. WOODSIEÆ.

Sori having a roundish indusium springing from the back of the veins.

11. WOODSIA.-Sori dorsal, with an indusium attached beneath them.

X. HYMENOPHYLLEÆ.

Sori produced at the end of the veins, and projecting from the margin, and surrounded by urn-shaped and 2-valved membranes.

12. TRICHOMANES.-Sori marginal, covered by urnshaped expansions of the frond.

13. HYMENOPHYLLUM.-Nori marginal, surrounded by 2-valved expansions of the frond.

OSMUNDACEÆ.

Fronds circinate, sori destitute of an elastic ring, and bursting vertically by two regular valves. 14. OSMUNDA. The only genus.

OPHIOGLOSSACEÆ.

Young fronds folded up straight, the sori without an elastic ring, and 2-valved.

15. BOTRYCHIUM.

Sori in irregularly branched clusters on a separate branch of the frond.

16. OPHIOGLOSSUM.-Sori sessile, in 2-ranked simple spikes on a separate frond.

In order to facilitate finding the name of a fern, we add the following analytical index, for the general plan of which we are indebted to Mr. Bentham's admirable" Handbook of the British Flora."*

1

21

3

Fructification in a terminal spike or panicle. The frond either leaf-like, or bearing a leaf in the lower part.... 2 Fructification in a little cup or involucre at the edge of the frond.....

4 Fructification on the back or under-side of some or all the fronds

5 Fronds twice-pinnate, usually two or more feet high, the fructification forming a panicle at their extremity.

OSMUNDA.

3

Fronds stem-like, not 6 inches high, with a terminal spike or panicle. (Spike simple. Leaf entire

OPHIOGLOSSUM. Spike branched into a panicle. Leaf pinnate. BOTRYCHIUM. Fronds numerous, scarcely 2 inches high, pinnate, with few deeply-lobed segments. Involucre ovate, 2-lobed. HYMENOPHYLLUM, Fronds 6 or 8 inches high, two or three times pinnate, with crowded segments. Involucre cup-shaped. TRICHOMANES.

* Published by Lovell Reeve, Henrietta-street, London.