Get complete information on the Range of Vegetative Structure of Alage

(1) Unicellular Algae:

These are of following two types:

(a) Motile:

In these algae movement takes place by flagella e.g. Chlamydomonas.

(b) Non-motile: e.g. Chlorella.

(2) Multicellular Algae: These are of following kind:

(a) Colonial:

In these algae, definite number of cells are found and these are motile, e.g. Volvox. This type of colony is known as motile colony. But a different kind of colony, coccoid colony is also found is multicellular algae. Number of cells in these colonies is indefinite and they are non motile e.g. Hydrodictyon.

(b) Aggregation:

In these algae cells are found in the form of indefinite colony. These are of two types:

(i) Palmelloid forms:

Algae cells in these are surrounded by a viscous mucilalginous substance e.g. Tetraspora.

(ii) Dendroid colony:

Cells of these forms produce mucilaginous substance and are folded in such a manner that they look like branches of a plant, e.g. Prasinocladus.

(c) Filamentous:

These are of following types:

(i) Simple unbranched filaments, e.g. Ulothrix.

(ii) Simple branched filaments, e.g. Cladophora.

(iii) Heterotrichous-Thallus consists of two parts, i.e. horizontally running main shoot/trichome and a vertical erect trichome/shoot e.g. Draparnaldiopsis, Coleochaete.

(d) Pseudoparenchymatous:

These algae are characterized by uniaxial filaments, e.g. Polysiphonia and multiaxial filaments e.g. Nemalion.

(e) Siphonous:

These algae consists of multinucleate tube like cells having no septa, e.g. Vaucheria.

(f) Parenchymatous:

In these algae, cell division takes place on different sides with the result that they become parenchymatous, e.g. Ulva.

Reproduction in Algae:

Reproduction in algae takes place by following methods:

(A) Vegetative

(B) Asexual

(C) Sexual.

(A) Vegetative Reproduction:

It is a simple process of reproduction in algae. By this process thallus divides into small fragments and each part later on gives rise to a new plant. This process is termed Fragmentation. In class Myxophyceae it takes place by hormogones.

(B) Asexual Reproduction:

In this process some cells or protoplasm of few cells of the plant divides to form a small sized structure, the spore. Each spore is liberated from the mother cell and gives rise to a new plant. It generally takes place by the following method:

(i) By Zoospores:

In this process, under favourable conditions biciliated (e.g. Ulothrix), tetr-aciliate (e.g. Ulothrix) or multiciliate (e.g. Oedogonium) zoospores are formed and on bursting of mother cells (300 sporangium) come out and give rise to new plant.

(ii) By Aplanospore:

In this case the protoplasm gets separated from cell wall to form one or more thin-walled, nonciliated aplanospores and each aplanospore gives rise to a new plant, e.g. Chlorella.

(iii) By Hypnospore:

In this process under unfavourable conditions the protoplasm of the cell separates from the cell wall and collects in the centre. These are non-motile and thick-walled. They give birth to new plant on the commencement of favourable conditions, e.g. Vaucheria.

(iv) By Akinete:

In this process, entire cell becomes thick. Akinetes are formed under unfavourable conditions and on commencement of favourable conditions each akinete develop into a new plant e.g. Cladophora.

(v) Palmella Stage:

On the approach of dry conditions, zoospores or aplanospores do not come outside the mother cell but get surrounded by mucilaginous sheath. The division continues with the result they take the shape of a colony. This is known as palmella stage. Under favourable conditions, they come out. Each zoospore or aplanospore gives rise to a new plant, e.g. Chlamydomonas.

(vi) By Endospores:

In most of the members of Myxophyceae, development of large number of endospores takes place inside the mother cell. Endospores gives rise to a new plant under favourable conditions.

(vii) By Autospores:

In some algae, the resting spores develop into new plants inside the mother cell, e.g. Chlorococcus.

(viii) By Cysts:

In some algae under unfavourable conditions and abundant food supply, the thallus divides into multinucleate and thick walled smaller segments, which are termed cysts. In favourable conditions cysts give rise to new plants, e.g. Vaucheria.

(C) Sexual Reproduction:

Sexual reproduction takes place by fusion of gametes. These gametes develop in gametangia. This is of following types.

(i) Isogamous:

In some algae the gametes are similar in their external morphology and size. In this type (+) and (-) strain gametes fuse together to form zygospore. Isogametes may be motile (zoogametes) e.g. Chalmydomonas debaryanum and Ulothrix or nonmotile (aplanogametes) e.g. Spirogyra.

(ii) Atiisogamous:

In some algae the gametes are similar in their external morphology but they differ in behaviour and size. The larger gamete is passive and it is known as macrogamete. The smaller gamete is active and is known as microgamete. The fusion of these two gives zygote which Jater on undergoes reduction divisions to form new plants e.g. Chlamydomonas braunii.

(iii) Oogamous :

In this type of sexual reproduction, fusion of small, biciliate or multiciliate and active male gamete with large non-ciliated and passive female gamete (which is retained within the oogonium either permanently or upto maturity) takes place and zygote (oospore) in formed, e.g. Oedogonium and Chlamydomonas coccifera.

Subdivision 2 ->Fungi:

(i) These are plants which lack chlorophyll but have a thallus-like plant body, i.e. they are non-green thallophytes.

(ii) These are nonvascular.

(iii) Not differentiated into root, shoot leaves.

(iv) They are parasitic or saprophytic and reproduce by spores.

The important classes of fungi are as follows:

Class 1: Schizomycetes

Class 2: Myxomycetes

Class 3: Phycomycetes

Class 4: Ascomycetes

Class 5: Basidiomycetes

Class 6: Deuteromycetes

Structure of Fungi:

The structure of plant body of fungi is simple. They range from unicellular, uninucleate forms to thread like structures called mycelium (plural) (singular-hypha) which is usually branched tube like structure, having protoplasm with reserve food and bounded by a wall of chitin. The protoplasm of the hypha may be continuous without cross walls and is called aseptate hypha or with transverse partitions or septa and is known as septate hypha. An aseptate hypha is nothing but a multinucleate tube like structure, called coenocyte. In aseptate hyphae, septa are formed when reproductive structures are produced.

In septate hypha, septa have a central pore and septa are thus perforated or porous. Sometimes pore may be absent in the septa (nonporous septa) or more than one pores may be present.

On the basis of number of nuclei in each cells, septate hyphae may be of 3 kinds, multinucleate, uninucleate (monokaryotic hyphae), with binucleate cells (dikaryotic hyphae) with each nucleus from different parent plant.

The fungus cell-wall is generally composed of a complex substance known as chitin which is often impregnated with some salts (not structurally identical with animal chitin). Formula of fungus chitin is (C₂₂H₅₄N₄O₂₁). In some fungi true cellulose has been detected. Sometimes a complex polysaccharide known as callose has also been reported.

Inside the cell, endoplasmic reticulum, dictyosomes, mitochondria, vacuoles, centroioles, storage product glycogen, alcohol mannitol and oils have been detected. Many hyphae together form the plant-body of fungi and is called mycelium. The mycelium may be hyaline or variously coloured. Sometimes the mycelium takes different forms which are as follows:

(1) Plectenchyma:

When hyphae of a mycelium grow together and intertwine with one another forming a thick woven tissue, it is called plectenchyma. Plectenchyma may be of two types :

(a) Rather loosely interwoven tissue whose hyphae component lie more or less parallel to each other and are recognizable-is known as prosenchyma or prosoplectenchyma.

(b) Hyphae lying adpressed to one another forming a compactly woven tissue whose hyphae component have lost their identity and appear
isodimetric and continuous in section resembling parenchyma of higher plants is known as pseudoparenchyma or paraplectenchyma.

(2) Sclerotia (Single Sclerotium):

In some fungi, the mycelium may pass into a dormant or resting stage by the formation of hard resting bodies resistant to unfavourable conditions, called scelerotium. The scelerotia may germinate upon the return of favourable conditions. Each sclerotium is composed of central prosenchymatous and peripheral pseudoparenchymatous tissue which is again surrounded by a ring of pigmented hyphae.

(3) Rhizomorph:

When the fungal hyphae aggregate together, behave as an organized unit to form a root like strand with a thick hard cortex and develop a growing tip somewhat resembling that of a root tip. It mainly serves the function of absorption.