9. Morphology of Flowering Plants - part 05 - FLOWER AND SEED

 

9. Morphology of Flowering Plants - part 05 - FLOWER AND SEED

Flower : 

• Flower is highly modified and condensed shoot meant for sexual reproduction.
• On the basis of position a flower can be 

1. axillary or 
   
2. terminal. 

• In a typical flower, the thalamus (Consists of four compactly arranged nodes and three highly condenseed internodes. 
• From each node of thalamus, a circle or whorl of modified leaves is produced. 
• A flower may show presence of bract at base of pedicel or over the pedicel, such a flower is said to be bracteate.
• A flower may not show presence of bract at base of pedicel, such a flower is said to be ebracteate.
• A flower with pedicel is said to be pedicellate flower.
• Without pedicel is called as sessile flower.
• Flower with bilateral symmetry or Clitoria is called zygomorphic flower e.g. Sweet pea.
• Flower with radial symmetry is called actinomorphic flower e.g. Sunflower.

Terminologies related to flower :

1. Complete : Presence of all four floral whorls.
2. Incomplete : Absence of any one of the floral whorl.
3. Perfect : Both androecium and gynoecium are present, also called as hermophrodite or bisexual flower.
4. Imperfect : Any one reproductive whorl is present also called as monophrodite or unisexual flower.
5. Unisexual : It can be either staminate (male)/ pistillate (female) flower
6. Neuter : When both reproductive whorls are absent, it is said to be neuter flower e.g. Ray floreti of sunflower.
7. Monoecious plant : Male and female reproductive flowers are borne on same plant. E.g. Maize.
8. Dioecious plant : Only one type of unisexual flowers are present on plant e.g. Date palm.

a. Insertion of floral whorls : 

• The position and arrangement of rest of the floral whorls with respect to gynoecium on the thalamus is known as insertion of floral whorls. 
• In a typical flower thalamus consist of four compactly arranged nodes and three internods. 
• Slope of thalamus decides insertion of floral whorls.

a. Hypogyny : 

• When the convex or conical thalamus is present in flower, ovary occupies the highest position while other floral parts are below ovary. 
• Ovary is said to be superior and flower is called as hypogynous flower. 
• E.g. Brinjal, Mustard, China rose etc. 
• It is denoted as G in floral formula.

b. Perigyny :

• When cup shaped or saucer shaped thalamus is present in a flower, ovary and other floral parts occupy about same position.Such an ovary is said to be semi- superior or semi-inferior. 
• All floral whorls are at the rim of thalamus. 
• Flower is perigynous 
• e.g. Rose, Pea, Bean, etc. 
• It is denoted as G- in floral formula.

c. Epigyny : 

• When thalamus completely encloses ovary and may show fusion with wall; the other floral parts occupy superior position and ovary becomes inferior. Such flower is said to be epigynous flower, 
• e.g. Sunflower, Guava etc. 
•  It is denoted as G - in floral formula.

b. Floral parts and their structure : 

• All floral parts develop from thalamus from different nodes. 
• From each node of thalamus circle or whorl of modified leaves is produced. Thalamus is called as torus or receptacle. 
• Thalamus is green in colour hence it can perform the process of photosynthesis.

1. Calyx (K) : 

• It is outermost floral whorl and individual members are known as sepals.
• Sepals are usually green in colour and perform photosynthesis. 
• If all the sepals are united, the condition is gamosepalous and if they are free, the condition is called as polysepalous.
• Gamosepalous calyx is found in china rose and polysepalous calyx is found in Brassica.
• The main function of sepals is to protect inner floral parts in bud condition. 
• Sometimes sepals become brightly coloured (petaloid sepals) and attract insects for pollination e.g.Canna, Mussaenda etc. 
• Calyx i.e. Sepals modify into hairy structures called as pappus. Such calyx helps in dispersal of seeds or fruits. E.g. Sonchus.

2. Corolla (C): 

• It is second floral whorl from outer side and variously coloured. 
• The individual member is called as petal. 
• Petals may be sweet to taste, posses scent, odour, aroma or fragrance etc. 
• The condition in which petals are free is said to be polypetalous (e.g. Rose) and if they are fused it is called as gamopetalous (e.g. Datura). 
• The main function of corolla is to attract different agencies for pollination.
  

Perianth (P) :

• Many times calyx and corolla remain undifferentiated. Such member is known as tepal. 
• The whorl of tepals is known as Perianth.
  

Do you know ?

• Mango is polygamous plant and produces all types of flowers, staminate, bisexual and neuter.

Arrangement of sepals, petals or tepals :
Valvate :

• Margins of sepals or petals remain either in contact or lie close to each other but do not overlap. 
• e.g. Calyx of Datura, Calotropis.

Twisted :

•  Margins of each sepal or petal is directed inwards and is overlapped. 
• While the other margin is directed outwards and overlap the margin of adjacent. 
• e.g. Corolla of China rose,Cotton etc.

Imbricate :

• One of the sepals or petals is internal and is overlapped at both the margins. 
• One is external i.e. completely outside Rest of the members. 
• Overlap and get overlapped. e.g. Cassia, Bauhinia, etc.

Vexillary :

•  Corolla is butterfly shaped and consists of five petals. 
• Outermost and largest is known as standard or vexillum, two lateral petals are wings and two smaller fused forming boat shaped structures keel. e.g Pisum sativum

• If all the tepals are free the condition is called as polyphyllous and if they are fused the condition is called as gamophyllous. 
• Sepaloid perianth shows green tepals while petaloid perianth brightly coloured tepals. 
• E.g. Lily, Amaranthus, Celosia, etc. 
• It protects other floral whorls. 
• Petaloid tepal helps in pollination and sepaloid tepals can perform photosynthesis.

Aestivation :

• The mode of arrangement of sepals, petals or tepals in a flower with respect to the members of same whorl is known as aestivation.

Epicalyx : 

• It is an additional whorl of sepal like structures formed by bractiole which occurs on the outside of calyx. 
• These are 5-8 in number. It is a characteristic feature of family - Malvaceae. 
• They are protective in function. e.g. Ladies finger

3. Androecium (A): 

• It is third floral whorl from outer side. 
• Androecium is male reproductive part of a flower. 
• The individual member is known as stamen. 
• If all the stamens are free the condition is polyandrous and if they are fused. (Cohesion = Fusion between members of a similar whorl.
• Adhesion = Fusion between members of dissimilar whorls)

Parts of Typical stamen :
1. Anther :

•  It is terminal in position. 
• Anther produces pollen grains. 
• It is usually bilobed bithecous, tetralocular/tetra sporangiate structure.  e.g. Datura. 
• In some plants it is monotheocus (single lobed). Bilocular bisporangiate structure e.g. Hibiscus.

2. Filament : 

• It is a stalk of stamen and bears anther at its tip. 
• It raises anther to a proper height for easy dispersal of pollen grains.

3. Connective : 

• It is in continuation with the filament. 
• It is similar to mid rib and connects  two anther lobes together and also with the filament.

Cohesion of stamens : 

• When stamens are united by filaments and anthers are free, the condition is adelphy.

Adhesion of stamens : 

• When the stamens are united to petals or tepals they are described as epipetalous e.g. Datura, Lily etc.

Syngeneious : 

• When anthers are united and filaments are free it is known as syngeny. 
• e.g. Sunflower

Synandrous  :

• Stamens are fused by both filaments and anthers in synandrous conditions e.g. Cucurbita.

4. Gynoecium (G): 

• It is the female reproductive part of flower and innermost in position.  It is also known as pistil. 
• The individual member of gynoecium is known as carpel. 
• The number of carpels may be one to many. 
• If all the carpels are fused the condition is described as syncarpous and if they are free the condition is described as apocarpous. 
• The polycarpellary gynoecium can be - 

1.  bicarpellary (two carpels e.g. Datura) 
2. tricarpellary (three carpels e.g. Cucurbita), 
3. pentacarpellery (five carpels e.g. Hibiscus) and so on.

• A typical carpel consists of three parts - 

1. stigma
2. style and 
3. ovary. 

1. Stigma :

• It is a terminal part of carpel which receives pollen grains during pollination.
• It helps in germination of pollen grain. 
• Stigma shows variation in structure to suit the pollinating agent. 

2. Style :

• It is narrow thread like structure that connects ovary with stigma. 

3. Ovary :

• It is basal swollen fertile part of the carpel. 
• Ovules are produced in ovary on a soft fertile tissue called placenta.

Placentation :

• The mode of arrangement of ovules on the placenta within the ovary is placentation.

Types of Placentation :

1. Marginal : Ovules are placed on the fused margins of unilocular ovary. e.g. Pea, Bean etc.
2. Axile : Ovules are placed on the central axis of a multilocular ovary. e.g. Chinarose, Cotton; etc
3. Parietal : Ovules are placed on the inner wall of unilocular ovary of multicarpellary syncarpus gynoecium. e.g. Papaya, Cucumber,
4. Basal : Single ovule is present at the base of unilocular inferior ovary. e.g. Sunflower, Rice, Wheat.

Free central : 

• Ovules are borne on central axis which is not attached to ovary wall. e.g. Fig.

 Seed : 

• Seed is a reproductive unit that developed from fertilized mature ovule. 
• The seed is made up of -

1. seed coat and one or 
2. two cotyledons. 

• Outer most covering of a seed is called seed coat, shows - 

1. outer layers called testa and
2. inner tegmen. 

• Hilum is a scar on the seed coat through which seed attach to the fruit. 
• Embryo of a seed enclosed within seed coat. 
• Embryonal axis consists of -

1. radicle and 
2. plumule. 

• The part of embryonal axis between cotyledon and plumule is epicotyl, while the part between cotyledons and radicle is hypocotyl. 
• The nutritive tissue in a seed called endosperm.