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Stamen Reduction:- Stamen reduction is the evolutionary process in which the number, size, or fertility of stamens decreases compared to the ancestral condition. It is a common evolutionary trend in flowering plants and is often associated with specialization for efficient pollination.
> Stamen reduction is the decrease in the number of stamens or the conversion of some stamens into sterile structures (staminodes) or their complete loss during floral evolution.
Types of Stamen Reduction:-
a. Numerical Reduction:- The number of stamens decreases from the ancestral condition.
Examples:-
> Many primitive flowers have numerous stamens (e.g., Magnolia).
> Advanced flowers may have: 10, 5, 4, 2, 1
Evolutionary sequence:- Numerous → 10 → 5 → 4 → 2 → 1
b. Functional Reduction:-
> Some stamens become sterile and no longer produce pollen.
> These sterile stamens are called staminodes.
Functions of staminodes:-
> Attract pollinators
> Protect nectar
> Support the pollination mechanism
Examples:-
> Canna – only one fertile stamen; others are petaloid staminodes.
> Cassia – some stamens are sterile.
c. Structural Reduction:- Stamens become smaller, fused, or modified.
Examples:-
> Short filaments
> Reduced anthers
> Petaloid stamens
Evolutionary Trend:-
Primitive Flowers:-
> Numerous free stamens
> Spiral arrangement
> Large androecium
Advanced Flowers:-
> Few stamens
> Fixed number
> Fusion of stamens
> Sterile stamens (staminodes)
> Sometimes only one fertile stamen
Causes of Stamen Reduction:-
> Adaptation to specialized pollinators
> Conservation of plant energy
> Increased pollination efficiency
> Evolution toward floral specialization
> Synchronization with stigma position
Carpel evolution:- 
i. Conduplicate theory:- According to the most widely accepted hypothesis, the carpel constitutes a modified, conduplicate megasporophyll bearing two, adaxial rows of ovules (Figure 6.9D). Recall that a “megasporophyll” is a modified leaf that bears megasporangia, which in the seed plants are components of the ovules and seeds;
ii. Appendicular theory:- This theory was put forwarded by De Candolle, Van Teighem and others and
supported by Eames (1961). According to this theory the inferior ovary has developed as a result of
the fusion of the bases of sepals, petals and stamens and as such appended to the axis of the flower
which has nothing to do with the formation of the ovary wall. Eames stated that due to evolution,
inferior ovary was developed from the superior one by the process of gradual fusion of the bases of
sepals, petals and stamens and adnation of the same to the gynoecium wall which indicate the
superiority of inferior vary over inferior ovary.
iii. Receptacular theory:- According to Schleiden and others, the receptacle of the flower has become
the instrumental in the formation of the inferior condition of the ovary. This has achieved through the
gradual sinking of the ovary to the deep cup shaped receptacle with the process of invagination of the
tip of the thalamus. After sinking down of the ovary the bases of sepals, petals and stamens have been
fused much in the same manner as in case of the appendicular theory.
Conduplicate Closure of Carpel:- Conduplicate closure of the carpel is the process by which a leaf-like carpel (megasporophyll) folds longitudinally along its midrib, bringing its two margins together. The margins then fuse, enclosing the ovules within a closed ovary.
> The term conduplicate means folded lengthwise along the midrib with the two halves facing each other.
Process of Conduplicate Closure:-
> A young carpel begins as a leaf-like structure (megasporophyll).
> The carpel folds inward along its midrib (conduplicate folding).
> The right and left margins of the folded carpel come together.
> These margins fuse, forming the ventral suture.
> The ovules, originally borne on the margins, become enclosed within the ovary.
> The enclosed structure develops into the ovary, while the upper part differentiates into the style and stigma.
U-Type Placenta (U-shaped Placenta):- A U-type placenta is a type of placenta formed during the development of a conduplicate (folded) carpel, where the placental tissue bends into a U-shaped structure inside the ovary. The ovules are attached along the inner sides of this U-shaped placenta.
> This type of placenta provides evidence that the carpel is morphologically a folded megasporophyll (leaf).
Formation of U-Type Placenta:-
> The young carpel originates as a leaf-like megasporophyll.
> Ovules develop along the margins of the carpel.
> The carpel folds longitudinally (conduplicate folding).
> The margins fuse to form the ventral suture.
> During development, the fused placental region curves inward, forming a U-shaped placenta.
> Ovules remain attached to the inner surface of the U-shaped placental tissue.
Ultra functional changes in tapetum:-
Tapetum:-
> A tapetum is the deepest layer of the anther, which encompasses the sporogenous tissue. The sporogenous tissue produces microspores that supply enzymes and nutrition for pollen development. Tapetum is mostly multinucleated due to mitotic cell division. Abnormal cell division can also lead to tapetum polyploidy.
> The tapetum is a huge structure, and thus can absorb food and provide nutrition to the development of the pollen grains. They also aid the regulatory molecules that help in the formation of the pollen grains. The cells of tapetum have dense cytoplasm.
Structure of Tapetum:-
Tapetum is a thick single-celled nutritive layer found behind the epidermis and endodermis. Their cells are initially diploid in nature but can become polyploid due to abnormal cell division. Their primary role is to absorb nutrition from the middle layer, and provide it to the microsporocytes. Also, the tapetum cells can secrete enzymes and hormones. The tapetum layer is almost lost in the mature anther.
Types of Tapetum:-
i. Secretory or Glandular Tapetum:- They surround the anther locule. This type of secretory tapetum is more common in angiosperms.
ii. Amoeboid or Plasmodial Tapetum:- After the disintegration of the tapetal cell wall, a multinucleate structure, along with the cell protoplast called the plasmodium tapetum, is formed.

Role of Tapetum in Pollen Development:-
i. Tapetum provides nutrition for the developing pollen grains.
ii. They also act as a precursor source for the pollen wall or pollen coat.
iii. It transports supplements to the anthers.
iv. Pollenkitt is also formed by the tapetal cells around the microsporocytes. This pollenkitt is responsible for nutrition and pollen development.
v. The tapetal cells act as a precursor to sporopollenin. The outer wall of pollen grains contains a chemical called sporopollenin that protects the pollen from harsh external factors.
vi. Tapetum expels Ubisch bodies, which helps thicken the pollen grain membrane. These ubisch bodies or orbicules are a part of the sporopollenin.
vii. Also, it secretes the callase enzyme that breaks the callose compounds used to unite four pollens (pollen tetrad). Thus, they allow pollens from a tetrad to be separated.

Synergids:- Synergids are two specialized haploid cells present in the egg apparatus of the mature embryo sac (female gametophyte) of flowering plants. They are located one on each side of the egg cell at the micropylar end and play an essential role in guiding the pollen tube for fertilization.
Position:-
> Located at the micropylar end of the embryo sac.
> Lie adjacent to the egg cell.
> Together with the egg cell, they form the egg apparatus.
Structure:-
> Usually two in number.
> Haploid (n) in chromosome number.
> Thin-walled, elongated or pear-shaped cells.
> Each contains:
    - A prominent nucleus
    - Dense cytoplasm
    -Large vacuole
> The wall facing the micropyle has a specialized thickening called the filiform apparatus.
Functions of Synergids:-
> Guide the pollen tube toward the egg apparatus by releasing attractant molecules.
> Receive the pollen tube at the micropylar end.
> One synergid usually degenerates before or during pollen tube entry, allowing the pollen tube to discharge the two male gametes.
> Assist in double fertilization by ensuring proper delivery of the male gametes.
> Provide nutritional and physiological support to the egg cell.
Endothelium:- It is a specialized single layer of nutritive cells that develops from the inner epidermis of the integument surrounding the embryo sac in many flowering plants. It is also called the integumentary tapetum because it functions similarly to the tapetum of the anther.
Development:-
> Originates from the inner epidermal layer of the inner integument.
> Develops as the embryo sac enlarges.
> Cells become elongated, dense, and metabolically active.
> Usually degenerates after embryo development.
Functions:-
> Provides nutrition to the developing embryo sac and embryo.
> Transfers nutrients from the integuments to the embryo sac.
> Helps in the growth and maturation of the female gametophyte.
> Supports embryo and endosperm development after fertilization.
> May store proteins, starch, and lipids temporarily.
Characteristics:-
> Single layer of living cells.
> Rich in cytoplasm and nuclei.
> Highly metabolically active.
> Similar in function to the anther tapetum.
> Common in many families such as Asteraceae, Solanaceae, and Rubiaceae.
Importance:-
> Essential for proper seed development.
> Ensures adequate nutrient supply to the embryo sac.
> Plays a significant role in successful fertilization and embryogenesis.
Obturator:- The obturator is a specialized group of cells or tissue present near the micropyle of the ovule in many flowering plants (angiosperms). It develops from the placenta, funiculus, or ovary wall and plays an important role in guiding the pollen tube toward the embryo sac for successful fertilization.
Functions of the Obturator:-
> Guides the pollen tube from the style to the micropyle of the ovule.
> Secretes mucilaginous substances that facilitate pollen tube growth.
> Provides nutrients to the growing pollen tube.
> Ensures successful fertilization by directing the pollen tube accurately to the embryo sac.
> Degenerates after fertilization, as its function is completed.
Role in Plant Development:-
> Develops during ovule maturation.
> Forms a bridge between the transmitting tissue of the style and the ovule.
> Enhances the efficiency of double fertilization in angiosperms.
> Supports seed development indirectly by ensuring successful fertilization.
Characteristics:-
> Usually composed of glandular or secretory cells.
> Rich in cytoplasm and metabolic activity.
> Temporary tissue that disappears after fertilization.
> Common in many families such as Asteraceae, Euphorbiaceae, and Rubiaceae.
Importance:-
> Increases the chances of successful fertilization.
> Helps maintain pollen tube viability.
> Essential for proper pollen tube guidance in species where it is present.

1. बीजाणुदभिदीय स्वअनिषेच्यता (Sporophytic Self Incompatibility):- जब स्वअनिषेच्यता पौधे के जीन प्रारूप द्वारा निर्धारित होती है तो इसे बीजाणुदभिदीय स्वअनिषेच्यता कहते हैं। इसमें मादा जनक पौधे या वर्तिकाग्र के जीन प्रारूप की तुलना नर जनक पौधे के जीन प्रारूप से की जाती है। 50℅ या 100℅ समानता होने पर निषेचन नहीं होता है तथा केवल 100℅ असमानता होने पर ही निषेचन होता है। जैसा कि नीचे diagram में प्रदर्शित किया गया है।

(When self incompatibility is determined by the genotype of the plant, it is called sporophytic self incompatibility. In this, the genotype of the female parent plant or stigma is compared to the genotype of the male parent plant. Fertilization does not occur if there is a 50℅ or 100℅ equality, and fertilization occurs only if there is a 100℅ inequality. As shown in the diagram below.)

   

उदाहरण (Examples):- सरसों, शलजम, गोभी आदि।

(Mustard, Turnip, Cabage, Cauliflower etc.)

Bud pollination:- It is the transfer of pollen to the stigma before the flower opens, while it is still in the bud stage. This technique is commonly used in plant breeding and genetics to ensure controlled pollination and prevent unwanted pollen from reaching the stigma.
Steps in bud pollination:-
> Select a mature flower bud that has not yet opened.
> Remove the anthers (male parts) if controlled cross-pollination is desired (emasculation).
> Apply pollen from the chosen parent plant to the stigma.
> Cover the pollinated bud with a paper or cloth bag to prevent contamination by unwanted pollen.
> Allow the flower to develop into fruit and seeds.
Importance:-
> Prevents self-pollination.
> Produces desired hybrids in plant breeding.
> Helps develop improved crop varieties with desirable traits such as higher yield or disease resistance.
Pollination in Salvia (Lever Mechanism):- Salvia is pollinated mainly by bees (entomophily) and shows a unique lever mechanism that promotes cross-pollination.
Mechanism:-
> The flower is bilabiate (two-lipped) and protandrous, meaning the anthers mature before the stigma, reducing self-pollination.
> It has two stamens with a long connective. Each stamen has:
> An upper fertile anther lobe containing pollen.
> A lower sterile anther lobe.
> When a bee enters the flower to suck nectar, it pushes against the sterile lobe.
> This acts like a lever, causing the fertile anther lobe to swing downward and dust pollen onto the back of the bee.
> When the bee visits another flower in the female stage, the mature stigma bends into the same position where pollen was deposited on the bee's back.
> The pollen is transferred to the stigma, completing cross-pollination.
Importance:-
> Ensures efficient cross-pollination.
> Minimizes self-pollination because of protandry.
> Increases genetic variation and reproductive success.
Development of Embryo in Monocot Plants:-
> In monocotyledonous plants, a good deal of variation is found in the stages of development of embryo. It is rather difficult to find a single plant in which the development of embryo may be considered as typical of monocotyledons. Development of embryo in Sagittaria (family, Allismaceae) has close resemblance to that in other monocots and is thus described here.
> Soon after fertilization, the fertilized egg or oospore greatly enlarges in size and divides transversely to form a 3-celled proembryo. These three cells are basal, middle and terminal. The basal cell, which is cut off towards the micropylar end, enlarges very much and forms major portion of the suspensor. The middle cell undergoes repeated transverse and vertical divisions thus differentiating few suspensor cells, radicle, plumule and hypocotyl. The terminal cell also undergoes a number of divisions in various planes and forms a single cotyledon.
> Here the cotyledon is a terminal structure and the plumule is laterally situated in a depression. In some monocots, like Colocasia, there is no suspensor in the embryo. Suspensor usually pushes the embryo into the endosperm from where the former gets nourishment. The suspensor may also serve as haustorium to absorb food from the nucelius. In some monocotyledonous plants like Agapanthus (family, Liliaceae) two cotyledons are formed instead of one.
Composite Endosperm:- Composite endosperm is a condition in which more than one embryo sac contributes to the formation of a single endosperm. This usually occurs due to the fusion of two or more embryo sacs or their polar nuclei before fertilization.
Formation:-
> Two or more embryo sacs develop close together.
> Their polar nuclei fuse with each other.
> One male gamete fertilizes the fused polar nuclei.
> A composite endosperm develops from the resulting primary endosperm nucleus.
Characteristics:-
> Formed from multiple embryo sacs.
> Usually polyploid because it contains nuclei from more than one embryo sac.
> It is a rare phenomenon in flowering plants.
Example:- Reported in Citrus species where adjacent embryo sacs may contribute to a common endosperm.

अपस्थानिक भ्रूणता (Adventive Embryony):- जब भ्रूण का विकास बीजाण्ड की किसी कायिक कोशिका (अध्यावरण या बीजाण्डकाय या निभाग) से बिना भ्रूणकोष बने होता है तो इसे अपस्थानिक भ्रूणता कहते हैं। जैसा कि नीचे diagram में प्रदर्शित किया गया है। उदाहरण:- नींबू, आम आदि।

(When the embryo develops from a vegetative cell of ovule (integument or nucellus or challaza) without the formation of embryo sac, it is called adventive embryony. As shown in the diagram below. Examples: Lemon, mango etc.)

द्विबीजाणुकता (Diplospory):- जब भ्रूणकोष का विकास द्विगुणित गुरुबीजाणु से होता है तो इसे द्विबीजाणुकता कहते हैं। गुरुबीजाणु का निर्माण बिना अर्धसूत्री विभाजन के होने के कारण यह द्विगुणित होता है। अत: भ्रूणकोष की प्रत्येक कोशिका भी द्विगुणित होती है। जैसा कि नीचे diagram में प्रदर्शित किया गया है।

(When the embryo sac develops from a diploid megaspore, it is called as diplospory. Megaspore is diploid because it is formed by mitosis instead of meiosis. Therefore, each cell in the embryo sac is also diploid. As shown in the diagram below.)

 भ्रूण का विकास निषेचन के बिना होता है। भ्रूण का विकास भ्रूणकोष की कौनसी कोशिका से होता है, इस आधार पर द्विबीजाणुकता 2 प्रकार की होती है-

(Embryo development occurs without fertilization. Depending upon the embryo develops from which cell of the embryo sac, there are 2 types of diplospory -)

i. अनिषेकजनन (Parthenogenesis)

ii. अपयुग्मन (Apogamy)

i. अनिषेकजनन (Parthenogenesis):- जब भ्रूण का विकास अण्ड कोशिका से होता है तो इसे अनिषेकजनन कहते है। जैसा कि नीचे diagram में प्रदर्शित किया गया है। उदाहरण:- Taraxacum (घास)

[When the embryo develops from the egg cell, it is called parthenogenesis. As shown in the diagram below. Example: - Taraxacum (grass)]

ii. अपयुग्मन (Apogamy):- जब भ्रूण का विकास प्रतिमुखी कोशिका या सहायक कोशिका से होता है तो इसे अपयुग्मन कहते हैं। जैसा कि नीचे diagram में प्रदर्शित किया गया है। उदाहरण:- प्याज

(When the embryo develops from the antipodal cell or the synergid, it is called apogamy. As shown in the diagram below. Example: - Onion)