An Introduction to Nature-studyStenhouse, E. (Ernest)
History
An Introduction to Nature-study
Stenhouse, E. (Ernest)
Natural history -- Study and teaching; Nature study
The leaves or fronds of the male-fern arise near the
growing-point (the upper end) of the stem. Leaves of almost all ages
are present. Those which surround the growing-point are mere rudiments;
while slightly older ones (Fig. 146, 1, a) are tightly
rolled up into a coil. During their growth the coils unfold, the inside of the
coil becoming the upper surface of the leaf. A fully expanded leaf is
roughly triangular in shape. The leaf-stalk and the midrib are covered
[Pg 187]
with brown, scaly hairs; and the blade of the leaf is divided into
several distinct leaflets, which are arranged on the midrib in two
rows. The leaflets are also in many cases sub-divided into separate
segments.
The spores.—On the lower surface of many of the segments of a
male-fern frond may be seen a number of small, brown, kidney-shaped
scales (Fig. 146, 3, a). Each scale is attached to
the leaf by a short stalk, and the structure thus bears a rough resemblance to a
little umbrella. Attached to the bottom of the short “handle” of the
“umbrella” are several tiny boxes, somewhat like pill-boxes. These are
shown at b (Fig. 146, 3), and highly
magnified at 4 and 5. Fig. 146, 6,
represents a single box, more highly magnified. When ripe, each
box contains about fifty minute grains, which may thus be likened to
the pills in the pill-boxes. These “pills” are called spores.
Summing up thus far, we may say that the spores are formed in
spore-boxes, which are attached by stalks to the lower surface of the
frond, each group of spore-boxes being covered by a protective scale.
The scattering of the spores.—When the spores are ripe, each
box (Fig. 146, 6) becomes dry, and is ultimately burst by
the sudden straightening of a spring (c) which is coiled round its edge.
The force of the uncoiling of the spring is sufficient to jerk the spores
(d) out of the box into the air, and they may be carried for some
distance by the wind before they at length reach the ground. Once
there, however, each spore, under favourable conditions, begins to
grow, and gives rise to a plant which, curiously enough, is not in the
least like the parent fern plant which produced the spore.
The difference between a spore and a seed.—It is important to
notice that the spore is produced by a purely non-sexual process. In
this respect it differs widely from the seed of a flowering plant,
[Pg 188]
which, it will be remembered (p. 92), results from
the union of the living matter of a pollen grain with that of an ovule.
Fig. 147.—The Male-Fern. A, Prothallus seen
from below; an, male organs; ar, female organs; rh, hairs. B,
Prothallus with young fern attached to it; b, the first leaf; w,
the primary root (about 5 times nat. size).
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