Reproduction : Reproduction is the process in living organisms to produce more organisms exactly like themselves.
Asexual reproduction : The process by which reproduction takes place without the fusion of gametes is called asexual reproduction.
Zoospores : Zoospores are the motile spores provided with cilia or flagella and which can swim freely in water e.g., Ulothrix, Vaucheria, etc.
Aplanospores : Aplanospores are the non-motile spores. They are devoid of cilia or flagella which are commonly found in terrestrial plants.
Significance of Asexual Reproduction :
1. In asexual reproduction many offsprings can be produced from an individual parent.
2. It is a simple and easier method of reproduction.
3. Helps an individual to regenerate overcoming unfavourable conditions.
Vegetative reproduction : In vegetative reproduction daughter plants are produced simply from the vegetative parts of a plant.
Fission : Fission is the process in which unicellular plants reproduce by cell division.
Binary fission : When two daughter plants are produced from a single plant it is called binary fission e.g., cosmarium, yeast, bacteria, etc.
Multiple fission : When a plant by repeated division gives rise to large number of daugher plants then it is called multiple fission e.g., Gloeocapsa.
Budding : It is the process in which unicellular plants like yeast develop one or more bud-like outgrowth from any portion of their body surface.
Fragmentation : Fragmentation is the process of breakdown of a multicellular plant body into a number of portions. e.g., Oscillatoria, Spirogyra etc.
Bulbils : In some plants, some lower flowers of inflorescence undergo modification to become small multicellular bodies known as bulbils e.g., Globba bulbifera, garlic, etc.
Adventitious buds : In Bryophyllum, Crassula, etc. a series of adventitious buds formed on the leaf margins, which usually develop into new individuals.
Leaf-tip : Certain ferns like Adiantum caudatum (walking fern) propagate vegetatively with the help of their leaf-tip.
Tuberous roots : Shatamuli, Dahlia, etc. reproduce vegetatively by means of tuberous roots (adventitious roots).
Underground stems : Many herbaceous flowering plants reproduce vegetatively by means of underground stems, e.g., Rhizome of ginger, Tuber of potato, Bulb of onion, garlic and corn of ol.
Sub-aerial stems : Sub-aerial stems of some plants which grow either along the soil or water surface produce daughter plants, which on detachment from the parent plant develop into the new plants e.g., Runner of Oxalis (wood sorrel), Centella (Indian penny wort), Offset of Pistia (water lettuce), Stolon of Mentha, Fragaria (strawberry) and Sucker of Chrysan-themum.
Significance of Vegetative Reproduction :
1. Vegetative reproduction is a simple and rapid method of reproduction.
2. Daughter individuals are like their parents.
3. Survival chances are more.
4. Good quality individuals are produced easily from good parental varieties.
Artificial or Induced methods of vegetative reproduction
1. Cutting : Mature stem of a plant bearing nodes and lateral buds can be cut and planted in moist soil. Examples—Sugarcane, Rose, China rose, Moringa (drum stick), Chrysanthemum, Dahlia etc., are reproduced by stem cutting.
2. Layering : Layering is the method in which the lower branch of a plant is bent down and kept below moist soil. In the buried region of the branch roots develop after a few weeks. It is then cut out from the parent plant and grown separately. Regular watering should be done to get good results. Examples—Rose, China rose, Lemon, Jasmine, etc.
3. Air layering or Gootee : In case of air layering a branch of a flowering and fruiting plant is injured carefully either by girdling or by cutting part way through a sharp angle. After that the wounded part of the branch is covered by means of cow-dung, manured clay soil and hay or hessian. This is known as gootee. Examples—Mango, Guava, Litchi, Lemon, etc.
4. Grafting : It is the method of growing of a cut piece of one plant (Scion) from a superior variety of plant over the cut branch of another rooted plant (Stock) of plant of same species. Examples—Mango, Litchi, Guava, etc.
5. Budding : It is a special type of grafting in which a shield-shaped piece of bark bearing a single bud is used as scion, which is placed in a T-shaped cut, done in the bark of the stock.
Inflorescence
Peduncle : Peduncle is the modified stem that bears flowers and helps in reproduction.
Inflorescence : The mode of development and arrangement of flowers on the peduncle is called ‘inflorescence’.
Pedicels : The flowers are attached to the peduncle with their stalks. These stalks are called ‘pedicels’.
Sessile : In some flowers the pedicels are absent and they are called sessile.
Terminal inflorescences : This develops from the apices of main stem of branches e.g., Crotalaria and Croton.
Axillary inflorescences : They are borne at the axils of leaves, e.g., Dolchos.
Intercalary Inflorescence : This type of inflorescence is borne at the internodes. After the formation of inflorescence, again the stem continues its growth. e.g., Callistemon.
Type of Inflorscences
I. Racemose or Indefinite Inflorescences
The peduncle grows indefinitely and produces a number of flowers directly or indirectly on its branches in acropetal manner.
(A) Pedicellate Racemose Inflorescences :
1. Simple Raceme e.g., Crotalaria and Tephrosia.
2. Compound Raceme e.g. Mangifera and Yucca.
3. Simple Corymb e.g., Gynandropis and Cassia.
4. Compound Corymb e.g., Brassica, Oleracea botrytis (Cauliflower)
5. Simple Umbel e.g., Allium cepa and Centella asiatica.
6. Compound Umbel e.g., Criadrum sativum and Daucus carota.
(B) Sessile Racemose Inflorescences :
1. Simple Spike e.g., Achyranthus and Amaranthus.
2. Compound Spike e.g., Triticum and Oryza.
3. Catkin e.g., Casuarina and Axalypha.
4. Simple Spadix e.g., Colocasia.
5. Compound Spadix e.g., Cocos nucifera, Musa.
6. Head or Capitulum or Anthodium e.g., Helianthus and Tridax.
7. Compound Head e.g., Echinops.
II. Cymose or Definite Inflorescence
Due to the development of a flower at its apex the growth of the penduncle is stopped. The bracts on the axis below this flower produce branches. These branches also terminate into a single flower.
1. Solitary cyme e.g., Hibiscus rosasinensis, Datura Gossypium.
2. Cymule e.g., Jasminum and Bougainvillea.
3. Monochasial cyme.
(i) Helicoid cyme e.g., mamelia and Begonia.
(ii) Scorpioid cyme e.g., Heliotropium and Solanum.
4. Dichasial cyme e.g., Clerodendron and Ispomoea.
5. Polychasial cyme e.g., Nerium and Plumeria.
III. Mixed Inflorescence
It is a type of inflorescence which shows both the characters of recemose and cymose types. e.g., Thyrsus.
IV. Special Type of Inflorescences
1. Verticellaster e.g., Leucas.
2. Cyathium e.g., Euphorbia, Poinsettia.
3. Hypanthodium e.g., Ficus species.
Flower
Flower is a modified and condensed shoot from which reproduction takes place. In a typical flower there are four types of floral leaves. They are sepals, petals, stamens and carpels. The first and second whorls of floral leaves namely sepals and petals are called ‘non-essential organs’. The floral leaves of third and fourth whorls namely stemens and carpels are called ‘essential organs’. Seed is produced from flower.
1. Monoecious : In this both male and female flowers are borne on the same plant, e.g., Cocos Nucliferia.
2. Dioecious : In this male and female flowers are borne on different plants, e.g., Borassus and Vallisnaria.
3. Polygamous : It is the condition in which unisexual and bisexual flowers are borne on the same plant, e.g., Mangifera and Polygonum.
Symmetry of Flower
(a) Acyclic or Spiral : There is a spiral arrangement of the floral parts on the conical or convex thalamus. e.g., Maganolia.
(b) Hemicyclic : It is an arrangement in which perianth lobes are arranged in whorls or circles but stamens and carpels are arranged spirally. e.g., Annona and Polyalthia.
(c) Cyclic : Cyclic arrangement is one in which different floral parts are arranged in circles on the thalamus. e.g., Hibiscus and Datura.
Merosity
(a) Isomerous : In this each whorl of a flower, similar number of floral parts or in multiples of that number are present.
1. Dimerous Two or in multiples of two.
2. Trimerous Three or in multiples of three.
3. Tetramerous Four or in multiples of four.
4. Pentamerous Five or in multiples of five.
5. Polymerous More than five.
(b) Anisomerous : In this, the floral parts in different whorls like sepals, petals, stamens and carpels are in different numbers. e.g., Achras sapota.
Structural Symmetry
(a) Actinomorphic flower : In it, various organs of each whorl in a flower are arranged symmetrically so that the flower can be divided longitudinally into two equal halves on any plane. e.g., Hibiscus.
(b) Zygomorphic flower : The floral organs in any whorl of a flower are arranged in a different way so that the flower can be cut into two equal halves only in one plane. e.g., Dolichos and Ocimum.
(c) Asymmetric flower : In a asymmetric flower, the flower cannot be cut into two equal halves in any plane because of the arrangement of floral organs in various whorls in different ways. e.g., Canna indica.
Bract : Bracts are the leaf-like structures on the peduncle. Flowers are borne only in the axils of bracts. These bracts protect the flowers in bud condition.
(a) Foliaceous bracts : These bracts are developed into coloured petal-like structures e.g., Adathoda and Acalypha.
(b) Petaloid bracts : Bracts are developed into coloured petal-like structures. e.g., Bougainvillea and Poinsettia.
(c) Involucre of bracts : The bracts of the flowers present in the outer whorl of an inflorescence are fused to give protection to it. e.g., Helianthus and Allium.
(d) Scaly bracts : Bracts are reduced to scale like strctures. e.g., Helianthus and Tridax (The scaly bracts of disc flowes are called ‘chaff’).
(e) Glumes : Glumes are the reduced bracts present on the axis of spikelets. They are of two types—1. Sterile bracts (Glumes) and 2. Fertile bracts (Lemma) e.g., Oryza sativa.
(f) Spathe : It is a modified expanded bract which covers and protects the inflorescence. e.g., Musa and Colocasia.
(g) Epicalyx : Epicalyx bracts are arranged in a circle, below the calyx. e.g., Hibiscus.
Thalamus or Receptacle or Torus : Thalamus is the condensed axis of the flower. It contains four condensed nodes, at which calyx, corolla, androecium and gynoecium are developed in four whorls. Internodes are very clearly seen in some flowers.
1. Anthophore : The internode of thalamus is present between calyx and corolla and it is developed into a stalk like structure. e.g., Silence.
2. Androphore : The internode of the thalamus between corolla and androcieum developed into a stalk like structure. e.g., Gynandropsis.
3. Gynophore : The internode between androecium and gynoecium develops into a stalk like structure in some flowers e.g., Capparis and Nelumbium. In Gynandropsis both androphore and gynophore are present.
4. Gynandrophore : On the axis of the flower the internode is like stalk and bears both androecium and gynoecium at its apex. e.g., Passiflora.
5. Carpophore : Thalamus which connects the carpels, grows into the gynoecium as a stalk like structures. e.g., Coriandrum.
6. Disc : Below the gynoecium the floral axis is present like a small disc e.g., Citrus species.
Perianth : Perianth is constituted by calyx and corolla together and it is a non-essential part of the flower. It protects the inner essential parts like androecium and gynoecium. Calyx appear green in colour and corolla is multicoloured.
1. Achlamydeous flowers : Perianth is not present and the flowers are called naked. e.g., Male and female flowers of cyanthium inflorescence.
2. Chlamydeous flowers : Flowers are with perianth.
(a) Monochlamydeous : Perianth is arranged in one whorl, e.g., Croton and Amaranthus.
(b) Dichlamydeous : Perianth is arranged in two whorls.
(i) Homochlamydeous : The flower has two similar whorls without any differentiation. They are called ‘tepals’ and are found mainly in monocot plants. e.g., Allium.
(ii) Heterochlamydeous : Perianth is arranged in two whorls. These can be differentiated into calyx and corolla. They are found usually in dicot plants. e.g., Datura and Hibiscus.
Aestivation
Aestivation is defined as the mode of arrangement of perianth lobes during bud condition.
1. Open : Perianth lobes are free and are arranged with wide gaps between them, e.g., Calyx of Brassica.
2. Valvate : In this the perianth lobes are arranged closely with small gaps between them. Valvate remain free or united. e.g., Calyx of Annona and Corolla of Brassica.
3. Twisted : In this type of aestivation the perianth lobes overlap each other. In this one margin is inside and the other one is outside. e.g., Corolla of Datura and Hibiscus.
4. Imbricate : This type of twisted aestivation is found in corolla. The overlapping of the petals is in 1 + 1 + 3 manner. i.e. the two margins of one perianth lobe are completely overlapped and the other one is external and in the remaining three perianth lobes one margin is overlapped by the next other. The imbricate aestivation is of two types.
5. Quincuncial : It is also a type of twisted aestivation. In this the perianth lobes overlap in 2 + 2 + 1 manner. In it the margins of two perianth lobes are completely overlapped, and the other two perianth lobes are external, and in the remaining one perianth lobe one margin is inside and other margin is outside. e.g. Calyx of Ipomoea and Catheranthus.
Calyx
Usually the sepals are the one essential parts of a flower which are thin, expanded and green coloured. They give protection to the flower during bud condition. If the sepals are free they are called ‘polysepalous’ (Annona) and if united they are called ‘gamosepalous’ (e.g. Hibiscus.)
Modification of Calyx
1. Petaloid : Sepals are coloured and appear like petals e.g. Tamarindus.
2. Pappus : Sepals are reduced to hair like structures called ‘pappus’. e.g., Sunflower family.
3. Spinous : On either side of the fruit, sepals are modified into two persustant spines, e.g. Trapa.
4. Hooded : One of the sepals covers the flower and is expanded, e.g., Aconitum.
5. Spurred : In the flower, one sepal is elongated into a tube and grows downwards. e.g., Impatiens.
6. Succulent : These are the succulent sepals storing water along with gelatinous substance. e.g., Dellinia.
Corolla
It is the second whorl of non-essential parts of a flower. The corolla lobes are called ‘petals’. They are coloured and attractive. They attract the insects and help in cross pollination. Some flowers do not have petals. The petals may be polypetalous or gamopetalous.
Shapes of Polypetalous Corollas
1. Sepaloid : Petals appear dark or light green coloured sepal-like structures. e.g., Annona and Artabotrys.
2. Saccate : Petals are tubular with an apical sac-like structure.
3. Spurred : Two petals grow tubular with a pointed base. In it the nectar is stored. e.g., Delphinum.
4. Coronary : Coronary is a crown-like structure formed at the tip of petals with specialised cells or scales. e.g., Passiflora, Nerium and Calotropis.
5. Cruciform : In this, the corolla contain four petals which are arranged in a cross-shaped manner. Each petal is clawed e.g., Brassica and Raphanus.
6. Rosaceous : In this the corolla contains five petals. Each petal is narrow at the base and broad, triangular at the apex. They are arranged symmetrically. e.g., Flowers of Malvaceae and Rosaceae.
7. Caryophyllaceous : In this there are five clawed petals arranged symmetrically. Each petal has a narrow stalk-like base, with an apex arranged at right angle to the base. e.g., Dianthus.
8. Papillionaceous : In this the corolla has 5 unequal petals. Of these the largest petal is arranged opposite to the axis. It is called ‘standard petal or vexillum’. On eitehr side of this, two ‘winged petals or alae’ are present. Anterior to these petals are present the remaining two petals whose ventral margins are fused and appear like the base of a boat. So, they are called ‘keel petal or carina’. e.g., Dolichos and Tephrosia.
Types of Gamopetalous and symmetrical corollas
1. Tabular : e.g., Disc florets of Asteraceae.
2. Companulate : e.g., Thevetia and Cucurbita.
3. Infundibuliform or Funnel-shaped : e.g., Datura and Petunia.
4. Rotate : e.g., Solanum.
5. Hypocrateriform or Salver shaped : e.g., Ixora and Catheranthus.
Types of Gamopetalous and asymmetrical corollas
1. Bilabiate : e.g., Ocimum
2. Ligulate : e.g., Tridax.
3. Personate : e.g., Crossandra and Acanthus.
Androecium
Androecium is the whorl of the flower and outer whorl of the essential parts containing stamens. These are the male reproductive organs. They are also called ‘microsporophylls’. They make pollen grains. The sterile stamens are called ‘staminodes’.
Parts of a stamen : Stamen has three parts—1. Filament 2. Anthers and 3. Connective. Attatchment of filament of anther lobes
1. Basifixed : The tip of the filament is fused with the base of anther lobe. e.g., Brassica and Datura.
2. Dorsifixed : On the mid dorsal side, the filament is attached to the anther e.g., Annona and Passiflora.
3. Adnate : The filament extends from the base to the apex of the anther lobes. e.g., Nelumbo.
4. Versatile : The apex of the filament is pointed and is attached to the back to the anther at a point, so that the anther lobes swing freely on any direction e.g., Oryza sativa.
Didynamous : Androecium has 4 stamens. Of these two are long and the other two are short. e.g., Ocimum.
Tetradynamous : Androecium has 6 stamens arranged in two whorls. The other two stamens are shorter and inner four are longer. e.g., Brassica.
Inserted stamens : In a few flowers the filaments are shorter than the petals. e.g., Datura and Dolichos.
Exterted stamens : In some flowers the filaments of the stamens are longer than the petals. e.g., Acacia arabica.
Arrangement of stamens
1. Haplostemonous : Alternate to the petals, all the stamens in a flower are arranged in one whorl. e.g., Solanum.
2. Diplostemonous : All the stamens in a flower are arranged in two whorls and outer whorl of stamens alternate with the petals. e.g., Cassia sps.
3. Obdiplostemonous : Stamens are arranged in two whorls and outer whorl is opposite to corolla lobes. e.g., Murraya exotica.
Number of stamens
1. Monandrous It is with one stamen e.g., Poinsettia.
2. Diandrous It is with two stamens e.g., Members of Acanthacease
3. Triandrous It is with three stamens e.g., Member of Monocots.
4. Tetrandrous It is with four stamens e.g., Ocimum
5. Pentandrous It is with five stamens e.g., Datura.
6. Hexandrous It is with six stamens e.g., Brassica.
7. Polyandrous It is with many stamens e.g., Members of Malcacease.
Cohesion of stamens : It includes the fusion among filaments, or anther lobes or both.
(i) Monadelphous : The filaments of all the stamens are fused to form only one bundle, e.g., Hibiscus.
(ii) Diadelphous : Out of 10 stamens in a flower, the filaments of 9 stamens are fused to form one bundle and the 10th remains free as a second bundle e.g., Dolichos.
(iii) Polyadelphous : The stamens are united to form many bundles by fusion of their filaments .e.g., Cieba pentandra.
Syngenesious : The anther lobes of all the stamens are fused, leaving their filaments free e.g., Disc florets of Tridax and Helianthus.
Synandry : The anthers are fused completely, e.g., Cucurbita.
Adhesion : Adhesion is the fusion of stamens with other parts of the flower arranged in different whorls like calyx, corolla and gynoecium. It is of three types.
(i) Episepalous : Stamens are fused to the sepals of outer whorl, e.g., Members of Proteaceae.
(ii) Epipetalous : Stamens attached to the corolla lobes.
(iii) Epiphyllous or Epitepalous : Stamens attached to the inner margins of perianth lobes e.g., Asparagus.
(iv) Gynostegium : Stamens are fused to the stagmas of gynoecium e.g., Caltropis.
Dehiscence of Anthers
1. Longitudinal : e.g., Datura.
2. Transverse : e.g., Hibiscus.
3. Valvular : e.g., Cassytha.
4. Porous : e.g., Solanum and Cassia.
Gynoecium
Gynoecium is the female reproductive organ and is the fourth whorl of the flower. It’s also considered as the inner whorl of the essential organs, formed from carpels. Carpels are called ‘megasporophylls’. They take part in sexual reproduction and produce fruits and seeds.
Structure of Gynoecium : Gynoecium contains three parts.
(a) Ovary which is basal swollen part.
(b) Style which is elongated apex of the ovary.
(c) Stigma is the tip of the style.
Ovary : Ovary is the basal swollen part of gynoecium, formed due to infoldings of the carpets. It consists of tone to any carpets. Each carpet is a modified leaf, known as ‘megasporophyll’.
Number of Carpels
1. Monocarpellary ovary with only carpel e.g., Dolichos
2. Bicarpellary ovary with two carpels e.g., Brassica
3. Tricarpellary ovary with three carpels e.g., Ricinus
4. Tetracarpellary ovary with four carpels e.g., Oenothera
5. Pentacarpellary ovary with five carpels e.g., Hibiscus
6. Multicarpellary ovary with many carpels e.g., Annona, Abutilon.
Fusion of Carpels
Apocarpous : The carpels present on the thalmus remain free. e.g., Nelumbo, Michelia, Rosa and Cedum.
Sub-apocarpous : The carpels present inside the ovary are partly attached and partly free e.g., Dianthus the ovaries are attached, but styles and stigmas are free. Hibiscus ovary and style are united, leaving the stigmas free. Calotropis only stigmas are attached, but ovary and styles remain free. Catheranthus styles and stigmas are united, but the ovaries remain free.
Syncarpous ovary : The carpels of the gynoecium are adhered as a single structure. The cavities present in the carpels are called ‘locules’. The number of locules differs from species to species.
(a) Unilocular with one locute e.g., Dolichos.
(b) Bilocular with two locules e.g., Solanum
(c) Trilocular with three locules e.g., Allium
(d) Tetralocular with four locules e.g., Ipomoea
(e) Pentalocular with five locules e.g., Hibiscus
(f) Multilocular with many locules e.g., Abutilon
Placentation
One or more ovules are present in the ovary. The mode of arrangement of ovules on the placenta called ‘placentation’.
1. Marginal placentation : e.g., Dolichos and Pisum.
2. Perietal placentation : e.g., Brassica.
3. Axile placentation : e.g., Hibiscus and Citrus.
4. Free central placentation : e.g., Dianthus.
5. Basal placentation : e.g., Tridax and Helianthus.
6. Apical or Pendulous placentation: e.g., Nelumbo.
7. Superficial placentation : e.g., Nymphaea.
Style : Style is an elongated, tubular, stalk like structure developing from the gynoecium.
(i) Terminal style : The style developed from the apical part of the ovary. e.g., Hibiscus.
(ii) Lateral style : This arises from the lateral side of the ovary. e.g., Mangifera.
(iii) Gynobasic style : Gynobasic style arises directly from the base of the ovary e.g., Ocimum.
Stigma : Stigma is the terminal part of the style. This receives pollen grains at the time of pollination.
1. Capitate : Round or gap like stigma e.g., Citrus.
2. Plumose : Stigma is feather-like e.g., Oryza.
3. Bifid : Stigma is forked-like. e.g., Tridax.
4. Dumb-bell shaped : Dumb-bell shaped stigma. e.g., Catheranthus.
5. Discoid : Stigma is disc shaped. e.g., Melia.
6. Funnel shaped : Funnel shaped stigma e.g., Crocus.
7. Linear : Long and narrow stigma. e.g., Acacia.
8. Radiate hook like : Stigma is hook shaped having radiating septate e.g., Papaver.
Pollination
Pollination : Pollination is the process in which pollen grains are transfered from the stamens to the stigma.
1. Cleistogamy : In this the pollination occurs in unopened flowers. e.g., Commelina benghalensis.
2. Chasmogamy : Chasmogamy is the pollination in flowers after their opening. It is the most common pollination in all types of flowers.
(a) Self pollination : Self-pollination is the process of transfer of pollen grains from the stemens to the stigma of the same flower. This type of pollination is possible only in bisexual flowers.
(b) Cross pollination : Cross polination is the transfer of pollen grains from the stamens of one flower to the stigma of another flower of the same species.
(i) Geitonogamy : In Geitonogamy pollen grains of the flower fall on the stigma of another flower present on the same plant.
(ii) Xenogamy : Pollen grains of one flower reach the stigma of another flower present on another plant. It is thought as true cross pollination.
Advantages of Cross
Pollination
1. In cross polination more seeds are produced.
2. The size of the seeds is large, healthy, germinate quickly and the yield is more.
3. These plants occupy much less space and the productivity of flowers is more.
4. In these plants genetic variations are more. The recombinations help these plants during the struggle for their survival.
5. These plants are resistant for diseases.
Contrivances for Cross Pollination
1. Dicliny or Unisexauality.
2. Dichogamy : In this, the androecium and gynoecium of a bisexual flower mature at different timings.
(a) Protandry : The maturity of androecium is earlier than gynoecium e.g., Helianthus, Clerodendron and Gossypium.
(b) Protogny : The gynoecium gets matured earlier than the stamens. e.g., Solanum, Scrophularia and Ficus.
3. Herkogamy : The herkogamy is the arrangement of male and female reproductive organs at different levels in a bisexual. In some flowers stigmas are longer than the stamens, e.g., Tridax and Hibiscus.
In some flowers the stigmas bend in opposite direction to the stamens, e.g., Gloriosa superba.
4. Heterostyly : The heterostyly is the presence of style in different length in the flowers of the same species.
(a) Diheterostyly : e.g., Primula and Oldenlandia.
(b) Triheterostyly : e.g., Linum.
5. Self sterility : e.g., Abutilon and Passiflora.
6. Pollen Prepotency : e.g. Dolichos.
7. Sesitive stigmas : e.g., Marthynia and Mimulus.
Contrivances which favour Self Pollination
1. Homogamy : To have pollination most of the plants produce bisexual flowers. Self pollination takes place when the stamens and ovary of these flowers mature at the same time e.g., Caltha and Ranunculus.
2. Incomplete Dichogamy : It is well known that dichogamy is a contrivancy for cross pollination but at some stages self pollination can also occur in some flowers. In protandrous flower, stamens mature earlier than gynoecium. At the final stages of stamen development the gynoecium comes to maturity and this stage, self pollination takes place.
3. Movement of floral parts : When inflorescence move by wind the pollen grains may fall on same stigma. In this condition self-pollination takes place.
4. Safety Mechanism : In safety mechanism generally cross-pollination fails to occur.
5. Cleistogamy : In cleistogamy self pollination frequently occurs. In these flowers the pollen released from the anthers are shed within the unopened flowers. This process is called cleistogamy. e.g. Commelina.
Agents for Cross Pollination
External agents like wind, water, animals etc. help in cross pllination. Pollen grains are not capable of reaching stigmas spontaneously.
Anemophily : The pollination occuring through wind is called ‘anemophily. Anemo means wind.
1. Suitable place for these plants is where the velocity of wind is more. The flowers are not showy.
2. The inflorescence is normally spike, catkin or spadix.
3. Flowers are bisexual and protandrous.
4. Perianth lobes may be reduced or absent.
5. Stamens show versatile fixation.
6. Flowers produce dry and light weight amount of pollen. This pollen can be dispersed to greater distances by wind currents.
7. Some times the pollen grains are released out by gun powder mecahinsm’. e.g., In Urtica and Pilea immediately after the flower bursts, the folded stamens become straight and disperse the pollen grains with a noise.
8. In some flowers the pollen grains are winged. e.g. Pinus.
Hydrophily : Hydrophily is the cross-pollination that takes place through water. It occurs in hydrophytes. Hydro means water.
Epihydrophily : The hydrophily that occurs on the surface of water is called as ‘epihydrophily’. e.g. Vallisnaria, Ruppia and Callitriche.
Hypohydrophily : This type of pollination occurs beneath the surface of water e.g. Zostera and Ceratophyllum.
Zoophily : Zoophily is the type of cross-pollination helped by animals.
Ornithophily : The birds are responsible for this type of cross-pollination. e.g. Bignonia, Erythrina, Sterilizia, Delonix etc.
Cheiropteriphily : The bats are responsible for this type of cross-pollination. e.g. Bauhinia megalandra, Oroxylum and Musa.
Malacophily : Malacophily-cross-pollination is by snails and slugs. e.g. Lamma.
Entomophily : This type of cross-pollination is by insects.
Characteristics of Entomophilous flowers
Size of the flowers : Some flowers are large and showy to attract the insects. This favours pollination.
Colour : Flowers become showy with coloured petals and perianth lobes.
Scent : Generally nocturnal flowers are not showy. They are white coloured and produce scent to attract insects. e.g. Cestrum nocturnum, Nyctanthus and Jasminum. Some flowers emit smell of rotten meat. Such flowers attract flies. e.g. Rafflesia and Sterculia.
Sometimes the scented leaves can also attract insects and help pollination e.g.: Coriandrum and Ocimum.
Rose flowers attract insects to favour pollination both by their attractive colours and scent.
Pollen : Some flowers produce large amount of pollen to attract insects. e.g. Argemone.
Nectar : Some flowers produce more honey to attract insects. These flowers are called ‘nectar’ flowers. e.g., Ixora.
Pollination—Types of Crops
Self-pollinating crops : e.g. Wheat, Groundnut, Chilies, Brinjal and Tomato.
Rarely self-pollinating crops : e.g. Paddy and Linseed.
Commonly cross-pollinating crops: e.g. Coriander, Carrot, Beet root and Mango.
Rarely cross-pollinating crops : e.g., Jowar and Cotton.
Embryology
Embryology is the branch of Biology that deals with the development of embryo from zygote. In plant kingdom, plants there are two stages, the sporophyte and the gametophyte which alternate with each other.
Sporophyte : it is a diploid (2x) stage. In the angiospermic plants the plant body belongs to this stage. It is developed from zygote. Vegetative and reproductive organs (flowers) develop on this plant.
Gametophyte : This is the highly reduced haploid stage of angiospermic plant. The pollen grain is called the ‘male gametophyte’ and the embryo sac is called the ‘female gametophyte’.
Micro sporophyll or Stamen : In flowering plants, the stamens or micro sporophylls are identified as male reproductive organs. Each stamen is made up of a filament, anther and a connective. The name ‘anther’ is used to the fertile part of the stamen. Each anther is made up of either one or two anther lobes. Each anther lobe contains two pollen chambers arranged longitudinally. Each pollen chamber represents a microsporangium. Thus a dithecous stamen consists of four microsporangia and a monothecous stamen contains two microsporangia respectively. The two anthor lobes are connected by a connective.
Anther wall : Anther wall consists of epidermis, endothecium, middle layers and tapetum.
Epidermis : Epidermis is a one-celled thick outer layer words as a protective layer.
Endothecium : Endothecium is found below the epidermis. The cells of this layer are expanded horizontally to form fibrous thickenings which are hygroscopic.
Middle layers : Just under the endothecium there are thin walled cells arranged in one to five layers.
Tapetum : The layer present below the middle layers is called tapetum. It is the innermost layer of anther wall which encircles the sporogenous tissue. It is a kind of nutritive tissue. It suplies nutritive materials to the developing sporogenous tissue. By the time the anther dehisces, the tapetum is completely utilised.
II. Sporogenous tissue : This tissue consists of fertile cells which directly act as microspore mother cells or produce microspore mother cells by mitotic divisions. Each microspore mother cell is diploid and undergoes meiosis to form four haploid microspores or pollen grains. The microspores are formed as tetrads and separate later.
Fruit
In flowering plants after fertilization the ovary develops as fruit and the ovules inside the ovary develop into seeds. Fruit may be defined as a fertilized and developed ovary.
Parthenocarpy
In some flowering plants the unfertilized ovary develops into a fruit. This phenomenon is called ‘Parthenocarpy’ and the fruits are called ‘Parthenocarpic fruits’. These fruits do not have seeds.
1. Genetic or Natural parthenocarpy : It is found in nature either by mutations or by hybridization e.g. Musa paradisiaca.
2. Environmental partheno carpy : The sexual reproduction obstructing environmental factors like fog, low tempeature etc. promote parthenocarpy e.g. Capsicum fruitiscense and Lycopersicum esculentum.
3. Chemically induced parthenocarpy : Use of hormones like auxins and gibberellins in low concentrations promotes parthenocarpy. This can also be induced by spraying or injecting diluted extraction of pollen grains. e.g. Strawberry and Fig.
Importance of Parthenocarpy : Parthenocarpic fruits have more pulp and are seedless fruits that is why they are widely used in the preparation of jams, jellys and juices. So, parthenocarpy is gaining importance in the fields of Horticulture and Pomology.
Types of Fruits
I. False Fruits
These fruits are developed from other floral parts except from the ovary such as calyx thalamus and pedicel, e.g.; Pyrusmalus, thalamus, Anacardium occidentalis, pedicel.
II. True Fruits
These fruits are produced from fertilized ovaries. The true fruit has two parts namely the fruit wall (pericarp) and the seed.
Simple Fruit
Simple fruit develops from a syncarpous ovary of single flower.
Fleshy fruits : In these fruits at the time of ripening the pericarp becomes fleshy.
Berry : A fleshy fruit having one or more seeds and develops from bi or multicarpellary, syncarpous ovary e.g. Solanum melongena, Lycopersicum esculentum and Musa paradisiaca.
The pericarp is differentiated into an outer thin epicarp, middle mesocarp and inner endocarp. The pulp is formed by the fusion of the mesocarp and endocarp.
Pome : A fleshy fruit produced from bi or multicarpellary, syncarpous and inferior ovary surrounded by fleshy thalamus e.g. Pyrus malus.
Pepo : Produced from tricarpellary, syncarpous, unilocular and inferior ovary.The pericarp is differentiated into an outer epicarp fused with hard sheath like thalamus to form a rind, fleshy mesocarp and smooth endocarp. Pepo contains many seeds and are arranged on parietal placentation. e.g. Cucumis sativa and Cucurbita maxima.
Hesperidium : Produced from multicarpellary, syncarpous, multiocular and superior ovary with seeds arranged on axile placentation. e.g., Citrus species.
Drupe : It is a fleshy fruit having one seed which develops from monocarpellary or multicarpellary, syncarpous, unilocular and superior ovary. The fruit has a stony endocarp. e.g. Magnifera indica and Cocos nucifera.
Dry fruits : In these fruits, on ripening, the pericarp remains dry and undifferentiated.
Dry Dehiscent : Fruits dehisce and liberate the seeds at maturity.
Follicle : Produced from a bicarpellary, sub-apocarpous ovary in which the carpels remain free. e.g. : Calotropis and Catharanthus.
Legume : It is produced from monocarpellary, unilocular and perigynous ovary at maturity. The fruit dehisces dorsiventrally into two halves liberating the seeds e.g., Dolichos lablab and Pisum sativum.
Silique : It is a long and narrow fruit developed from bicarpellary, syncarpous, superior ovary with parietal placentation. The ovary is unilocular but becomes bilocular due to the development of a false septum called ‘replum’. The seeds fuse on either side of the replum. At maturity the pericarp dehisces dorsoventrally from base to apex, leaving the seeds on the replum. e.g. Brassica.
Silicula : The silicula is a short and broad siliqua fruit which has limited number of seeds. e.g., Capsella bursa pastoris.
Capsule : It is a dry dehiscent fruit which develops from bi or multicarpellary syncarpous, uni or multilocular, superior or inferior ovary. At maturity it dehisces.
Septicidal capsule : The capsule dehisces along the septa between the locules into definite number of pieces equal to the number of carpels at maturity. e.g., Aristolochia.
Loculicidal capsule : The capsule dehisces through the middle portions of the locules at maturity e.g., Gossypium herbaceum and Abelmoschus esculentus.
Septifragal capsule : In this capsule fruit wall dehisces either by loculicidal or septicidal manner, leaving the seeds on central, swollen axis of the placenta. e.g., Datura.
Porous capsule : It is a cup-shaped fruit with a lid. In between the lid and the margin of the cup many pores are present. Through these proes seeds are dispersed at maturity. In the fruits developed from superior ovary, the pores are present on the upper side (e.g., Papaver), whereas in the fruits developed from inferior ovary the pores are present at the base of the capsule. e.g., Companula.
Pyxidium : This type of fruit is developed from superior ovary. It is a spherical shaped capsule in which the pericarp splits transversely. The upper part falls off as a lid and the seeds are left out in the basal cup like structure. e.g., Amaranthus.
(III) Dry Indehiscent Fruits
These dry fruits are generally one seeded and never dehisce even at maturity.
1. Achene : This dry indehiscent fruit is developed from monocarpellary, unilocular and superior ovary. The pericarp and seed coat remain free. Normally in aggregate fruits they remain as fruitlets. e.g. Clematis.
2. Caryopsis : It is similar to achene but the pericarp and seed coat fuse together. It is the characteristic fruit of the family Poaceae. e.g., Oryza and Triticum.
3. Cypsela : This fruit has only one seed developing from bicarpellary, syncarpous, unilocular and inferior ovary. This is characterised by persistent pappus like calyx. e.g., Tagetus patula.
4. Nut : It is a dry indehiscent fruit developing from bi or multicarpellary, syncarpous, unilocular and superior ovary. This has a stony pericarp. It encloses a single seed. The pericarp and the seed coat remain free. e.g., Anacardium occidentalis.
5. Samara : It is a dry winged indehiscent fruit developed from bicarpellary or tricarpellary, syncarpous and superior ovary. The wings are produced from the pericarp and they help in dispersal. e.g., Hiptage. Wings are developed from calyx in Gyrocar-pus, from the style in Bentilago and from both calyx and style in Shorea. In Acer double samara is present.
(IV) Schizocarpic Fruits
These fruits are the dry fruits which show the characters of both the dehiscent as well as indehiscent fruits.
1. Lomentum : This fruit is produced from monocarpellary ovary like a legume. At maturity the fruit dehisces on the sutures into many cocci. e.g., Acacia and Mimosa.
2. Cremocarp : It is produced from bicarpellary, syncarpous, bilocular and inferior ovary. At maturity the fruit dehisces into two one-seeded pericarps attached to the carpophore. e.g., Coriandrum sativum.
3. Carcerulus : It is a dry schizocarpic fruit developing from bicarpellary, syncarpous, tetralocular and superior ovary. At maturity the fruit dehisces into four nutlets. e.g., Ocimum.
4. Regma : It is a schizocarpic fruit which develops from tricarpellary, syncarpous, trilocular and superior ovary. At maturity the fruit splits into three one seeded cocci. e.g., Ricinus communis.
5. Schizocarp : This is produced from multicarpellary, syncarpous, multilocular and superior ovary. At maturity it splits into many cocci. e.g., Sida, Abutilon.
6. Double samara : This fruit is produced from bicarpellary, syncarpous and superior ovary. The fruit dehisces into two samara like cocci e.g., Acer.
Aggregate Fruits
True fruits are born out of a single flower. Flower is having multicarpellary, apocarpous ovary. Each carpel developed into a fruitlet. All these fruitlets are aggregated on a common pedicel (receptacle) to form a single aggregate fruit. the bunch of fruitlets is called ‘etaerio’.
Etaerio of Achenes—e.g. Naravelia, Straberry and Nelumblum
Etaerio of Berries—e.g., Polyalthia and Artabotrys
Etaerio of Drupes—e.g., Rubus
Etaerio of Follicies—e.g., Magnolia
Etaerio of Samaras—e.g., Acer
Compound Fruits or Multiple Fruits
These fruits are produced from whole of the inflorescence with its component parts.
1. Sorosis : It is a multiple fruit which develops from spike (Artocarpus—Jack fruit) or spadix (Monstera) or catkin inflorescence (Morus). These fruits remain fleshy (Ananas) sativus—Pineapple) or dry (Casuarina).
2. Syconus : It is a multiple fruit which is produced from hypanthodium inflorescence. e.g., Ficus benghalensis.
Edible parts of different fruits :
1. Apple—Thalamus
2. Banana—Mesocarp + Endocarp
3. Cashewnut—Fleshy pedicel + Cotyledons
4. Citrus—Juicy hairs in the endocarp
5. Cucurbita—Fleshy mesocarp and endocarp
6. Coconut—Endosperm (both cellular and liquid)
7. Jack fruit—Fleshy perianth and seeds
8. Pineapple—Axis, perianth and placenta
9. Brinjal—Whole fruit
10. Guava—Whole fruit
11. Dates—Pericarp
12. Grapes—Pericarp + Placenta
13. Mango—Mesocarp
14. Borassus—Mesocarp + Endosperm
15. Pulses—Seeds
16. Bean—Pericarp + Seeds
17. Cereals—Endosperm
18. Tamarindus—Mesocarp + Endocarp
19. Feronia—Mesocarp + Endocarp + Seeds
20. Punica granatum (Pomegranate)—Succulent testa of seeds
21. Pithecolobium—Fleshy aril
22. Mulberry—Whole fruit
23. Ficus—Inflorescence axis (receptable)
Dispersal of Fruits and Seeds
Fruits and seeds are dispersed to distant places in all flowering plants. This process is called dispersal of fruits and seeds. If they are not dispersed, the seeds fall directly below the mother plant and germinate. A struggle for existence ensues among the new plants. The fruit and seed dispersal helps mainly in reducing this struggle for existence, improving the plant population continuously and also in distributing the plant species to various places. The broadcast seeds germinate in the new areas and produce colonies where they get more opportunities for their survival.
In dehiscent fruit the pericarp breaks at maturity and disperses the seeds. But in indehiscent fruit, the entire fruit is dispersed from one place to another. This dispersal mechanism is brought about by some external agents like air, water, animals and mechanical devices. Accordingly the fruit and seed dispersal methods are of four types.
1. Dispersal by wind
2. Dispersal by water
3. Dispersal by animals and
4. Dispersal by mechanical devices.
Seed and its Germination
Dormancy : Inside a seed, the seed plant or embryo takes rest for certain period. The period of resting prior to germination is called dormancy.
Germination : Seed germination may be defined as the growth of an embryo or baby plant resulting in the rupture of the seed coat and emergence of the young plant.
Epigeal germination : During germination if the cotyledons are pushed upwards by the rapid elongation of the hypocotyl—germination is then said to be of epigeal type. This type of germination is noticed in bean, gourd, sunflower, cotton, castor, etc.
Hypogeal germination : In this type of germination cotyledons remain in the soil or just on its surface. The epicotyl, i.e., the portion of the axis lying immediately above the cotyledons, elongates and pushes the plumule upward. Here the cotyledons gradually dry up and fall off. Germination of this type is termed hypogeal. This can be seen in seeds of pea, mango, litchi, jack, groundnut, etc.
Viviparous germination : This is a special type of germination in which the seeds germinate within the fruit while it remains attached to the plant. This type of germination and is observed in plant growing in marshy saline areas; e.g., Sundri plant, growing in the Sunderbans.
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