Sporophyte of riccia
Mature Sporogonium:
The sporophyte of Riccia is represented by only a single globular capsule which
is found to be the simplest organisation among the bryophytes. Foot and seta
are completely absent
A mature sporogonium is represented only by spherical spore sac or capsule. It
lacks foot and seta.
It has a single-layered capsule wall which encloses spores. There are no
elaters. A bilayered calyptra forms a protective covering around the capsule.
The capsule wall and inner layer of calyptra break down before the spore
mother cells divide to form the spores. After meiosis the mass of spores lies free
in the outer layer of calyptra and mature sporogonium has no diploid structure.
The newly formed young gametophyte remains enclosed with in the old
gametophyte
(a)Riccia Bryophytes- In Riccia, zygote divides and redivides to farm a mass of spherical mass of 20-30 undifferentiated cells. Periclinal
segmentation forms
(b)an inner mass of cells called endothecium and outer single layer amohithecium. The amohithecium single layered capsule wall.
(c) The endothecium forms the central mass of sporogenous tissue.
Practically, all the sporogenous cells are fertile and develop into spores. However, few of them undergo degeneration to form the nurse
cells.
The Sporophyte of Riccia is the simplest among all the bryophytes and has the least amount of sterile cells.
(d)The entire embryo froms the spore producing capsule. There is not foot and Seta. It is just a spore producing organ without any
distributing function.
Sporogonium:
1. It is simple and made up of only capsule or spore-sac
2. Foot and seta are absent.
3. It remains embedded in the gametophyte, and it is a non-green structure, thus depending entirely on
the gametophyte for food.
4. Inside sporogonium are present many spore mother cells which remain surrounded by a capsule
wall and two-layered calyptra.
5. Spore mother cells divide reductionally, and each of them thus forms four haploid spores, arranged
tetrahedrally.
6. Prior to the formation of spores, the wall of the sporogonium as well as the inner layer of calyptra
dissolve, and thus only a single-layered calyptra is present outside the spores.
7. Elaters are absent (Fig. 163).
8. Neck of the long archegonium may remain outside for some time but it ultimately withers.
Structure of the spore
The mature spore is three layered. The outer most, cutinized layer
is exosporium, the middle layer is mesosporium which
is thick walled and consists of three concentric zones. The inner
most layer is endosporium.
The spore is the beginning of the gametophytic generation.
Spore:
1. It is the first cell of the gametophytic generation.
2. Shape of the spore is rounded or pyramidal.
3. Each spore is surrounded by a thick, black or sculptured wall.
4. Wall of the spore consists of three layers: outermost exine or
exosporium, which is thick and sculptured; middle thin mesosporium and:
innermost, thin intineor endosporium
5. Spores are unicellular and uninucleate structures.
6. In the cytoplasm are present many oil globules.
7. Spores germinate and develop into gametophyte plant of Riccia
