Riccia is a genus of liverworts in the order Marchantiales. These plants are small and thallose, that is not differentiated into root, stem and leaf. Depending on. Riccia is a thallose liverwort in which the vegetative plant, which is a gametophyte, generally forms rosettes due to the crowded growth of the thallus lobes this. Riccia description with images for under graduate students. the gametophytic phase of the life cycle ends with the formation of zygote.
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The axial cell cuts of a small cover cell at the tip. These phases alternate with each other. This zone represents the ventral tissue of the thallus and lies below the photosynthetic zone. In Riccia crystallina the scales are inconspicuous and absent. The wall of each pife spore is very unevenly thickened and it consists Of three layers, the outer exosporium which is thin, hard and cutinised; the middle mesosporium which is very thick and soft; and the inner endosporium which is membranous.
A vertical cross section of the thallus shows two distinct zones, viz. Neck of the archegonium consists of six vertical rows and each row consists six to nine cells. The apical part of the young rhizoids divides and re-divides to form a gemma like mass of cells in some species e. Antheridial chamber, in which an antheridium riccix, communicates with the clorsal surface of the thallus by terminal opening. The ventral side also bears scales which are formed of a single layer of cells and are arranged in two rows in the older parts of the thallus while in the younger parts these scales are in one row and in the apical region are crowded below the notch for the protection of the growing point.
Rhizoids develop in the light medium intensity. The male and female nuclei fuse together producing a single diploid nucleus. The act of fertilization also stimulates the division of the wall of the venter.
Riccia Structure, Life Cycle, Sexual and Asexual Reproduction
The mature sporogonia are embedded in the tissue of the thallus and are visible to the naked ridcia as small black dots on the thallus. Thus detached lobes develop into independent plants by apical growth.
Each spore remains surrounded by three layers i. Air chambers spaces help in the gaseous exchange. Rhizoids are nearly lacking in aquatic forms, but there are usually numerous unicellular rhizoids of two types on the ventral surface.
The main function of rhizoids is to anchor the thallus on the substratum and to absorb water and mineral nutrients from the soil.
Its cells divide and re-divide to form a mass of sporogenous cells sporocytes, Fig. When a spore falls riccai a suitable place, it germinates by the production of a long tube.
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Simultaneously the nucleus also becomes crescent shaped, homogeneous and ultimately comes in contact with the blepharoplast.
Apical cells of the antheridial wall get swollen by absorbing water. In the majority of species the assimilatory region is formed of vertical rows of cells which are about six to eight cells in height and are separated by large air spaces, the cells of these filaments are rich in chloroplasts as these form the main photosynthetic tissue.
Each archegonium develops from a superficial cell situated on the dorsal side about three or four cells away from the growing point. The last division in each androgonial cell is diagonal thus producing two androcytes antherozoid mother cells.
The spores are haploid as these have been produced after the reduction division in the spore mother cells. The lower storage region is a continuation of the upper assimilatory region and is parenchymatous.
Life Cycle of Riccia (With Diagram) | Hepaticopsida
In this article we will discuss about the g ametophytic phase, reproduction and sporophytic phase in the life cycle of riccia. Some species the assimilatory region is spongy being formed of irregularly placed air spaces which are separated from each other by single layered partitions whose cells are rich in chloroplasts. The venter goes on increasing in size along with the developing sporogonium, and in this way the mature sporogoniurn remains enclosed in the double layered wall of venter.
The following seven species have been commonly reported from the North Western Himalayas and the Punjab plains in Pakistan: The central cell llfe into an upper primary neck canal cell and a lower venter cell. It divides anticlinally and periclinally to form a two-layered calyptra along the developing sporophyte.
Its blepharoplast elongates into a cord and occupies about two-thirds of its part. On resumption of favourable conditions tubers produce new thalli. The male sex organ is the riccka while the female sex organ is the archegonium Sex organs develop in acropetal succession, ie.
In monoecious species alternate groups of antheridia and archegonia develop at a sufficient distance from the growing point. The lobes in Riccia fluitanswhich is an aquatic species, are narrow and ribbon-like having repeated dichotomous branches which do not form any rosetts, Numerous unicellular rhizoids are found ctcle to the ventral side of the thallus, these rhizoids are generally crowded in the middle part of the thallus and cgcle of two types i.
Several antherozoids may enter a fo archegonium but only one of them fuses with the egg for fertilization. Both the androcytes remain enclosed in the wall of the androcyte mother cell with one separate wall Fig. Each of the three peripheral initials divides by an anticlinal vertical division forming two cells.
Chapter 29 Reading Quiz About how many species of plants inhabit earth today? It is more a method of perennation rather than multiplication. Chinese Company introduces new low price Chinese electric car in Pakistan. A single-layered sterile jacket encloses the mass of androcytes which metamorphoses into antherozoids.
In spongy thallus of Riccia crystallina the assimilatory or photosynthetic cells form a loosely- arranged network enclosing large cyle spaces. A transverse division takes place in all the cells resulting in the ricciw of a lower and an upper group of cells. Both the male antheridia and cjcle archegonia reproductive organs are lif in acropetalous order on the dorsal side of the thallus in the median furrow. Asexual reproduction occurs by sporesby fragmentation of the rosettes, and by formation of apical tubers.
Published by Darrell Bradley Modified over 2 years ago.