me point of
this a bud appears to originate, which produces the first fern-leaf,
soon followed by a second and third, and so the stem and leaves of the
plant are set up.

[Illustration: Fig. 511. Lycopodium Carolinianum, of nearly natural
size. 512. Inside view of one of the bracts and spore-case, magnified.]

[Illustration: Fig. 513. Open 4-valved spore-case of a Selaginella, and
its four large spores (macrospores), magnified. 514. Macrospores of
another Selaginella. 515. Same separated.]

[Illustration: Fig. 516. Plant of Isoetes. 517. Base of a leaf and
contained sporocarp filled with microspores cut across, magnified. 518.
Same divided lengthwise, equally magnified; some microspores seen at the
left. 519. Section of a spore-case containing macrospores, equally
magnified; at the right three macrospores more magnified.]

490. Investigation of this prothallus under the microscope resulted in
the discovery of a wholly unsuspected kind of fertilization, taking
place at this germinating stage of the plant. On the under side of the
prothallus two kinds of organs appear (Fig. 510). One may be likened to
an open and depressed ovule, with a single cell at bottom answering to
nucleus; the other, to an anther; but instead of pollen, it discharges
corkscrew-shaped microscopic filaments, which bear some cilia of extreme
tenuity, by the rapid vibration of which the filaments move freely over
a wet surface. These filaments travel over the surface of the
prothallus, and even to other prothalli (for there are natural hybrid
Ferns), reach and enter the ovule-like cavities, and fertilize the
cell. This thereupon sets up a growth, forms a vegetable bud, and so
develops the new plant.

491. An essentially similar process of fertilization has been discovered
in the preceding and the following families of Pteridophytes; but it is
mostly subterranean and very difficult to observe.

492. =Club-Mosses or Lycopodiums.= Some of the common kinds, called
Ground Pine, are familiar, being largely used for Christmas wreaths and
other decoration. They are low evergreens, some creeping, all with
considerable wood in their stems: this thickly beset with small leaves.
In the axils of some of these leaves, or more commonly, in the axils of
peculiar leaves changed into bracts (as in Fig. 511, 512) spore-cases
appear, as roundish or kidney-shaped bodies, of firm texture, opening
round the top into two valves, and discharging a great quantity of a
ve