CHAPTER XXIII
PHENOGAMS AND CRYPTOGAMS
The plants thus far studied produce flowers; and the
flowers produce seeds by means of which the plant is propagated.
There are other plants,
however, that produce no seeds,
and these plants (including bacteria)
are probably more numerous
than the seed-bearing plants.
These plants propagate by means
of spores, which are generative cells, usually simple, containing no embryo.
These spores are very small,
and sometimes are not visible to
the naked eye.
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Fig. 254.—Christmas Fern.—Dryopteris acrostichoides; known also as Aspidium.
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Fig. 255.—Fruiting Frond of Christmas Fern.
Sori at a. One sorus with its indusium at b.
Prominent among the spore-propagated plants are ferns. The common Christmas fern (so called because it remains green during winter) is shown in Fig.254. The plant has no trunk. The leaves spring directly from the ground. The leaves of ferns are called fronds. They vary in shape, as other leaves do. Some of the fronds in Fig. 254 are seen to be narrower at the top. If these are examined more closely (Fig.255),
