he head or spike of spore-cases, with some of
the latter taken off. 495. View (more enlarged) of under side of the
shield-shaped body, bearing a circle of spore-cases. 496. One of the
latter detached and more magnified. 497. A spore with the attached arms
moistened. 498. Same when dry, the arms extended.]

[Illustration: Fig. 499. A Tree-Fern, Dicksonia arborescens, with a
young one near its base. In front a common herbaceous Fern (Polypodium
vulgare) with its creeping stem or rootstock.]

[Illustration: Fig. 500. A section of the trunk of a Tree-Fern.]

486. =Ferns, or Filices=, a most attractive family of plants, are very
numerous and varied. In warm and equable climates some rise into
forest-trees, with habit of Palms; but most of them are perennial herbs.
The wood of a Fern-trunk is very different, however, from that of a
palm, or of any exogenous stem either. A section is represented in Fig.
500. The curved plates of wood each terminate upward in a leaf-stalk.
The subterranean trunk or stem of any strong-growing herbaceous Fern
shows a similar structure. Most Ferns are circinate in the bud; that is,
are rolled up in the manner shown in Fig. 197. Uncoiling as they grow,
they have some likeness to a crosier.

[Illustration: Fig. 501. The Walking-Fern, Camptosorus, reduced in size,
showing its fruit-dots on the veins approximated in pairs. 502. A small
piece (pinnule) of a Shield-Fern: a row of fruit-dots on each side of
the midrib, each covered by its kidney-shaped indusium. 503. A
spore-case from the latter, just bursting by the partial straightening
of the incomplete ring; well magnified. 504. Three of the spores of 509,
more magnified. 505. Schizaea pusilla, a very small and simple-leaved
Fern, drawn nearly of natural size. 506. One of the lobes of its
fruit-bearing portion, magnified, bearing two rows of spore-cases. 507.
Spore-case of the latter, detached, opening lengthwise. 508.
Adder-tongue, Ophioglossum; spore-cases in a kind of spike: _a_, a
portion of the fruiting part, about natural size; showing two rows of
the firm spore-cases, which open transversely into two valves.]

487. The fructification of Ferns is borne on the back or under side of
the leaves. The early botanists thought this such a peculiarity that
they always called a Fern-leaf a FROND, and its petiole a STIPE. Usage
continues these terms, although they are superfluous. The fruit of Ferns
consists of SPORE-CASES, technically SPORANGIA, whi