for most of us flowers are a source of pleasure with their variety of shapes and vast range of colors they're used to brighten our Homes and Gardens and their bright blooms also bring color to our city streets but flowers are also the reproductive organs of the plant it's for this reason that scientists will work with flowers to breed new better and more valuable varieties of plants a flower is therefore not just decorative but plays an important part in plant reproduction the role the flower plays in reproduction is easier to see in the larger simpler flowers of the mini monocot edans the small number and large size of their flower parts allows us to easily illustrate their structure each flower has three [Music] seeps which overlap three petals inside the petals there are six stamms that produce pollen each Stam is attached to the flower by a [Music] filament the enlarged sack at the tip of the filament is called the anther inside the anther there are four microsporangia each microsporangium is nourished by a layer of of surrounding cells called the tetum a microsporangium consists of diploid sparite cells the cellulose walls of these cells are soon replaced by a layer of K each sparite now divides twice by meiosis this creates four haid microspore cells each with one set of chromosomes this group of adhering microspores is known as a tetrad soon the Kos is removed and sporopollenin begins to form on the surface of each cell the surrounding tetum now releases additional sporo poinin one area of each wall The sulcus Remains smooth receiving very little spor aolin however the rest of the wall is covered in a thick ornate coating of this tough resistant material each microspore nucleus now divides by mitosis the lower generative cell separates from the wall and moves into the cytoplasm of the larger tube cell this is the immature male and is known as a pollen grain before it is released the pollen grain accumulates nutrient reserves finally most of the water is lost and the pollen grain enters into a resting state before the anther releases the pollen the cells beneath the epidermis develop thickened walls this is called the endoth [Music] thesium when the pollen and the antha mature and dry out the endoth thesium shrinks this tears open the anther between each pair of microsporangia allowing the pollen to escape [Music] at the center of the flower there are three [Music] caral at the base of each carple there is an enlarged ovary a slender style extends from the ovary and at the tip of the style there is a stigma the three cares are fused together forming one stigma and a style with a central Canal the base of the canal leads into each of the three ovaries in the young carple small outgrows appear on the ovary wall each of these is a megasporangium two layers of cills the integuments grow over the megasporangium a small pore the micropile is the only area that remains uncovered by the integuments this entire structure is called an ovule inside the sporangium there is a single diploid sparite cell the diploid sparite divides by meiosis to form four haid nuclei each with one set of chromosomes in some plants such as lilium walls are not formed around these nuclei but in the majority of flowering plants walls are formed around each nucleus resulting in four megaspore cells three of these then degenerate the surviving Spore enlarges and the nucleus divides three times yielding eight haid nuclei two of these nuclei move towards the center these are known as the polar nuclei seven cells now form at the micropile end there is an egg cell and two Syed cells in the middle there is a central cell containing the two polar nuclei Above This the remaining nuclei form three antipodal cells this is the female gapy also known as the embryo sac this is contained within the megasporangium which is covered by the integuments of the ovule the OVU in turn is surrounded by the [Music] CLE the transfer of pollen to the receptor surface of the stigma is called pollination this happens by various means such as wind insects or other [Music] animals the poen grain now absorbs water and begins to swell a pollen tube soon emerges containing the tube nucleus and the generative cell the generative cell devised to form two sperm cells in order to reach the ovaries the pollen tube must now carry the sperm down the full length of the canal it does does this by first growing through the stigma to reach the surface of the canal directly below here it grows along the moist transmitting tissue which serves as a path to the ovary pollen tubes of a very fast rate of growth often several micrometers per minute this growth is localized at its tip vesicles containing wall material accumulate at the tip where they are required for wall growth behind this the cytoplasm flows around the cell in regular streams this is known as cytoplasmic streaming the two sperm cells and Tube nucleus continually move forward as the cell grows plugs of wall material called Kow for form which keep the cytoplasm close to the growing [Music] tip when the pollen tube reaches the base of the style it grows into one of the three [Music] ovaries [Music] inside the ovary the tube locates the two rows of [Music] ovules approaching an OVU the pollen tube grows into the micropile where it penetrates the [Music] megasporangium it then grows into one of the Syed cells releasing the two sperm one sperm fertilizes the egg cell forming a diploid zygote cell The second sperm fuses with the two polar nuclei forming a primary endosperm cell this double fertilization is characteristic of all angia sperms the ovary contains hundreds of ovules and each requires a pollen tube to be fertilized to accomplish this the style supports the growth of a large number of Po tues these grow down the style and enter each of the three over when the pollen tubes enter an ovary they each locate and fertilize an [Music] OVU each ovary now has many fertilized ovules which will develop into [Music] seeds after the ovules are fertilized the flower undergo several changes many parts begin to wither eventually these parts are sheded only the ovary remains healthy and firmly attached to the stem inside the ovary the ovules are now about to undergo many changes each ovil contains two fertilized cells the nucleus of the primary endosperm cell begins to divide to form endosperm tissue with no cell walls the zygo divides forming a large basil cell and a small apical cell the basil cell produces a chain of cells called a suspensor and the apical cell gives rise to an embryo the suspensor now begins to transport nutrients into the young embryo in monocot alans A Single Seed leaf for calan forms as it enlarges the embryo also received nutrients directly from the surrounding Ender sper during this time walls slowly form within the endosperm tissue a tiny Chute tip forms on one side of the embryo below this there is a stem called the hyper cotle at the base of the hyper cotle there is a root this is covered by a protective root cap in most monocot alans nutrients now begin to accumulate within the endosperm when nutrient accumulation is complete much of the water is removed and the embryo enters a state of dorcy however a different sequence of events takes place in the ovules of most dians in these ovules the growing seed leaves accumulate nutrients and absorb all of the endosperm as both types of ovules mature the integuments develop into a tough protective seed coat the OVU is now a seed at the same time that the OVU is changing into a seed the developing embryo is releasing hormones these stimulate the ovary to expand and make room for the enlarging ovules in this way the ovary wall expands and is transformed into a fruit in most lies the fruit is a tough dry capsule that tears open to release the seeds the seeds are soon disperse and will germinate to form new plants thus completing the life cycle we have seen that flowers capture pollen and ensure the success of fertilization and Seed formation in the Plant World reproduction by flowers is the most efficient it's therefore not surprising that a great variety of flowering plants dominate the landscape many of these attain great size but others are tiny and almost microscopic some flourish in places where water is scarce others thrive in ponds and lakes and from this vast variety we have by careful breeding developed all those plants which provide us with food [Music] with the great variety of flowering plants the world in which we live is indeed a very colorful [Music] place