Fig. 253.
Archegonium of riccia, showing
neck, venter, and the egg;
archegonium is partly
surrounded by the tissue of
the thallus.
(Riccia crystallina.)
Fig. 254.
Young embryo (sporogonium)
of riccia, within the
venter of the archegonium;
the latter has now two
layers of cells.
(Riccia crystallina.)
480. Sporogonium of riccia.—The fruit of riccia, which is developed from the fertilized egg in the archegonium, forms a rounded capsule still enclosed in the venter of the archegonium, which grows also to provide space for it. Therefore a section through the plant at this time, as described for the study of the archegonium, should show this capsule. The capsule then is a rounded mass of cells developed from the egg. A single outer layer of cells forms the wall, and therefore is sterile. All the inner cells, which are richer in protoplasm, divide into four cells each. Each of these cells becomes a spore with a thick wall, and is shaped like a triangular pyramid whose sides are of the same extent as the base (tetrahedral). These cells formed in fours are the spores. At this time the wall of the spore-case dissolves, the spores separate from each other and fill the now enlarged venter of the archegonium. When the thallus dies they are liberated, or escape between the loosely arranged cells of the upper surface.
Fig. 255.
Nearly mature sporogonium of Riccia
crystallina; mature spore at the right.
Fig. 256.
Riccia glauca; archegonium containing
nearly mature sporogonium. sg,
spore-producing cells surrounded by
single layer of sterile cells, the
wall of the sporogonium.
481. A new phase in plant life.—Thus we have here in the sporogonium of riccia a very interesting phase of plant life, in which the egg, after fertilization, instead of developing directly into the same phase of the plant on which it was formed, grows into a quite new phase, the sole function of which is the development of spores. Since the form of the plant on which the sexual organs are developed is called the gametophyte, this new phase in which the spores are developed is termed the sporophyte.