Fungi also have 3 types of reproductions:
(A) Vegetative (B) Asexual (C) Sexual
(A) Vegetative Reproduction:
Vegetative reproduction in fungi may be of following types:
Fragmentation of the vegetative hyphae may be accidental and fragments develop into new plants under favourable conditions.
In this, simple splitting of vegetative cells into two daughter cells takes place by constriction.
Some fungi produce small outgrowths i.e. buds from their vegetative body. Such buds receive one daughter nucleus as a result of division of the parent nucleus. Eventually the buds are cut off from parent cell and mature to form new individuals. The buds may remain attached to the parent cell for a long time resultating in the formation of a chain of buds (called pseudomycelium).
(iv) Oidium formation: In some fungi, the hyphae breakup into numerous small fragments known as oidia and give rise to new hyphae.
In some fungi, the hyphae forms under unfavourable conditions, thick walled resting resistant spores which later separate apart from each other. They may be terminal or intercalary. They may remain viable for several years. On return to favourable conditions they germinate to give rise to new individuals. Thus chlamydospores are organs of perennation.
(B) Asexual Reproduction:
This is of the following types:
(i) Zoospore formation:
Zoospores may be uniflagellate, e.g. Synchitrium or biflagellate e.g. Saprolgenia, Phythium and are thin walled uninucleate structures formed in zoosporangia. They germinate to give rise to new mycelium. Biflagellate zoospores are of two kinds, pearshaped or perform with two flagella placed at anterior end (primary zoospore) and kidney shaped or bean shaped, bearing two oppositely directed flagella inserted laterally in a furrow or concave side (secondary zoospores).
(ii) Aplanospore formation:
Aplanospores are thin-walled non-motile spores produced in a sporangium which after liberation give rise to new mycelium, e.g. Rhizopus, Mucor.
Conidia are non-motile thin walled exogenous spores produced on a condiophore. They are arranged in chains upon the conidiophore e.g. Aspergillus and Penicillium. They may also be produced singly on a conidiophore e.g. Phythium.
(C) Sexual Reproduction:
Sexual reproduction is reduced in fungi and take place by two fusing gametes. It includes 3 stages, which are as follows:
In this, there is union between two protoplasts which result in bringing the fusing nuclei of different parentage close together.
The two haploid nuclei which come together in plasmogamy fuse and thus a diploid zygote is produced.
In the zygote, reduction takes place, thus reducing the number of chromosomes to half. Sexual reproduction in fungi is of the following types:
(i) Planogametic Copulation:
This is the simplest type of sexual reproduction. In this process, fusion of two gametes of opposite sex or strains takes place. One or both of the fusing gametes are motile. It results in the formation of a diploid zygote. This process is usually of three types.
In this process fusing gametes are morphologically similar but physiologically dissimilar. These gametes are produced by different parents, e.g. Synchytrium.
When the fusing gametes are morphologically as well as physiologically different, the process is known as heterogamy. Heterogamous reproduction is of two types, anisogamous and oogamous. Anisogamy consists in the fusion of two gametes, the male gamete being more active and small while the female gamete is larger and less active e.g. Allomyces. In oogamy, the gametes are produced inside the morphologically different gametangia.
The male gametangia is smaller and called antheridium while the female gametangium is larger and is called oogonium. The antheridium bears smaller, active and motile gametes known as sperms while the oogonium bears non-motile, large egg.
(ii) Gametangial Contact:
In this process, two gametangia come in contact with one another. Either a passage is formed by dissolution of common wall at the point of contact or fertilization tube is developed to facilitate the migration of entire contents of male gametangium into the female gametangium. Both the gametangium never fuse together losing their identity.
(iii) Gametangial Copulation:
In this process, fusion of entire contents of two gametangia is accomplished either by dissolution of their common walls resulting in the formation of a single cell, in which protpolasts of two gametangia fuse or transfer of one entire protoplast of one gametangia into the other takes place through a pore developed in the gametangial wall at the point of contact. (Difference with heterogamy is that here two gametangia originate from two zoospores, whereas in heterogamy, two gametangia develop on somatic hyphae).
Some fungi produce many minute, spore like, single celled structure called spermatia (non-motile gametes). These structures are transferred through agencies like water, wind and insects to either special receptive hyphae or trichogyne of ascogonium. The contents migrate into recpetive structure. Thus dikaryotic condition is established.
This takes place in fungi where formation of gametes is absent. In such fungi, anastamoses takes place between somatic structures bearings nuclei of different parentage whereby nuclei of one passes into cooresponding somatic cell by dissolving the wall, thus establishing a dikaryotic condition.
Division 2 ->Bryophyta
(i) Most simple & primitive group of Embryophyta.
(ii) It includes 840 genera and 23,500 species.
(iii) Plants are very small and cosmopolitan.
(iv) Plant body is green thallus like without vascular tissues.
(v) Sex organs are multicellular & jacketed.
(vi) Asexual reproduction by mitospores is entirely absent.
(vii) Presence of distinct embryo stage in the life cycle is seen.
(viii) A heterologous type of alternation of generations occurs constantly.
(ix) The gametophyte is the conspicuous plant in the life cycle.
(x) The male reproductive structure is antheridium and female reproductive structure is archegonium.
Bryophyta can further be classified into:
Class 1: Hepaticae or Liverworts
Class 2: Musci or Mosses.