Function & Morphology of Flowers

Function

The biological function of a flower is to mediate the union of male and female gametes in order to produce seeds. The process begins with pollination, is followed by fertilization, and continues with the formation and dispersal of the seed.

Morphology

Flowering plants heterosporangiate (producing two types of reproductive spores). The pollen (male spores) and ovules (female spores) are produced in different organs, but the typical flower is a bisporangiate strobilus in that it contains both organs.

A flower is regarded as a modified stem with shortened internodes and bearing, at its nodes, structures that may be highly modified leaves. [1] In essence, a flower structure forms on a modified shoot or axis with an apical meristem that does not grow continuously (growth is determinate). The stem is called a pedicel, the end of which is the torus or receptacle. The parts of a flower are arranged in whorls on the torus. The four main parts or whorls (starting from the base of the flower or lowest node and working upwards) are as follows:

Anatomy of a Sarracenia flower. The umbrella shaped style is unique to this genus, and will look different in most flowers

• Calyx – the outer whorl of sepals; typically these are green, but are petal-like in some species.
• Corolla – the whorl of petals, which are usually thin, soft and colored to attract insects that help the process of pollination.
• Androecium (from Greek andros oikia: man's house) – one or two whorls of stamens, each a filament topped by an anther where pollen is produced. Pollen contains the male gametes.
• Gynoecium (from Greek gynaikos oikia: woman's house) – one or more pistils. The female reproductive organ is the carpel: this contains an ovary with ovules (which contain female gametes). A pistil may consist of a number of carpels merged together, in which case there is only one pistil to each flower, or of a single individual carpel (the flower is then called apocarpous). The sticky tip of the pistil, the stigma, is the receptor of pollen. The supportive stalk, the style becomes the pathway for pollen tubes to grow from pollen grains adhering to the stigma, to the ovules, carrying the reproductive material.

Although the floral structure described above is considered the "typical" structural plan, plant species show a wide variety of modifications from this plan. These modifications have significance in the evolution of flowering plants and are used extensively by botanists to establish relationships among plant species. For example, the two subclasses of flowering plants may be distinguished by the number of floral organs in each whorl: dicotyledons typically having 4 or 5 organs (or a multiple of 4 or 5) in each whorl and monocotyledons having three or some multiple of three. The number of carpels in a compound pistil may be only two, or otherwise not related to the above generalization for monocots and dicots.

This Crateva religiosa flower is perfect: it has both stamens (outer ring) and a pistil (center)

In the majority of species individual flowers have both pistils and stamens as described above. These flowers are described by botanists as being perfect, bisexual, or hermaphrodite. However, in some species of plants the flowers are imperfect or unisexual: having only either male (stamens) or female (pistil) parts. In the latter case, if an individual plant is either male or female the species is regarded as dioecious. However, where unisexual male and female flowers appear on the same plant, the species is considered monoecious.

Additional discussions on floral modifications from the basic plan are presented in the articles on each of the basic parts of the flower. In those species that have more than one flower on an axis—so-called composite flowers— the collection of flowers is termed an inflorescence; this term can also refer to the specific arrangements of flowers on a stem. In this regard, care must be exercised in considering what a ‘‘flower’’ is. In botanical terminology, a single daisy or sunflower for example, is not a flower but a flower head—an inflorescence composed of numerous tiny flowers (sometimes called florets). Each of these flowers may be anatomically as described above. Many flowers have a symmetry, if the perianth is bisected through the central axis from any point, symmetrical halves are produced - the flower is called regular or actinomorphic e.g. rose or trillium. When flowers are bisected and produce only one line that produces symmetrical halves the flower is said to be irregular or zygomorphic. e.g. snapdragon or most orchids.

Floral formula

A floral formula is a way to represent the structure of a flower using specific letters, numbers, and symbols. Typically, a general formula will be used to represent the flower structure of a plant family rather than a particular species. The following representations are used:

Ca = calyx (sepal whorl; e.g. Ca⁵ = 5 sepals)
Co = corolla (petal whorl; e.g., Co^3(x) = petals some multiple of three )
Z = add if zygomorphic (e.g., CoZ⁶ = zygomorphic with 6 petals)
A = androecium (whorl of stamens; e.g., A^∞ = many stamens)
G = gynoecium (carpel or carpels; e.g., G¹ = monocarpous)

x - to represent a "variable number"
∞ - to represent "many"

A floral formula would appear something like this:

Ca⁵Co⁵A^{10 - ∞}G¹

Several additional symbols are sometimes used (see [1]).

Keep Valentine's Day Flowers Alive Longer

Fresh flowers are a popular gift on holidays, with good reason--92% of American women can remember the last time they were given flowers, and fresh flowers have an immediate positive impact on happiness. Increase the lifespan of your beautiful flowers, and extend your good feelings, by following these easy steps!

• Handle your flowers carefully--they are delicate and living plants.
• Keep flowers in water, first removing any leaves that will be submerged.
• While holding the bottom of the stem, cut about an inch off the stem with a sharp, clean knife or clippers. This will allow water to pass more easily through the flower stem.
• Use a commercial flower food, properly mixed in your vase water. Make sure you follow the directions on the floral preservative packet--most packets are for either one pint or one quart of water. Bottled water can be used to increase water uptake.
• If your vase solution begins to become cloudy, re-cut the stems and place into a new vase solution.
• Keep flowers out of direct sunlight and in a cool place to help them retain moisture.
• Keep flowers away from heated surfaces to prevent wilting.
• Keep flowers away from cigarette smoke and ripening fruit, because they contain ethylene gas, which is harmful to flowers.

-- Terril Nell, Professor and Chair, Environmental Horticulture Department

The Science Of Love (the chemistry of romance)

The Science Of Love (the chemistry of romance)

Life, 22, 2, 38(1)
Feb, 1999
ISSN: 0024-3019

ABSTRACT:
Researchers believe that love at first sight is not just a cliche. A chemical reaction which may lead to romance can be created when one person first looks at another. A mix of natural chemicals and hormones may explain why opposites attract, mismatched couples success and some couples survive the worst situations.

TEXT:
The couples on the following pages prove what researchers now know: Romance, quite literally, requires a certain chemistry. Love at first sight is no apocryphal cliche. Writer Nuna Alberts reports that researchers now know why one glimpse of the right person can let off a chemical reaction leading to romance. But what happens after what? Why do some relationships succeed while others fizzle? That may be more magic than science. Claudia Glenn Dowling visits with 10 famous couples who have overcome time and trials: depression, the death of a child, cancer, the stress of public life. Through it all, their marriages have survived--even grown stronger. "Need is the thing that holds a marriage together over the long haul," says actor Carroll O'Connor. "If the need stops, the marriage stops."

Thirty-one-year-old Dana Commandatore claims she has never been the kind of woman men immediately notice. But one night last year, while at a singles bar with friends, she couldn't keep the opposite sex away. "Guys were coming up to me and getting very close, and I was like, 'Wow!'"
The New York City office manager, now in a committed relationship with one of the men she met that night, credits her ability to attract him that evening to a costly potion ($60 for a tenth of an ounce) called Falling in Love. Its manufacturer, Philosophy cosmetics, claims the concoction is laced with pheromones, those odorless airborne molecules, synthesized from human chemical secretions, that are purported to boost attractiveness. (And yes, it's available at a department store near you.)

Bunk? Sniff if you will. Many do. But whether one believes Commandatore is hopelessly susceptible or remarkably savvy, one thing is clear: New research in the field of love and attraction shows that
romance--long the domain of poets, philosophers and five-hankie movies--may be ruled as much by molecules as it is by emotion. In fact, scientists now believe that the impulse that drives us to mate, marry and remain monogamous is not a result of mere social convention: It is also a complex mix of naturally occurring chemicals and hormones--Cupid's elixirs, if you will--that helps guide us through life's most important decision. That physiological component, say the researchers, may help explain some of love's mysteries: why opposites attract, why so many seemingly mismatched couples succeed, why we stick together with partners through even the worst of times.

"When you fall in love or in lust, it isn't merely an emotional event," says Theresa Crenshaw, M.D., the Masters and Johnson-trained author of The Alchemy of Love and Lust. "Your body's hormones, each with unique contributions, get involved too."

Free will, of course, can't be discounted. If you like redheads, you like redheads. If you're a sucker for a beautiful voice, the man who croons "Night and Day" to you has an edge. But doctors have long known that even that most primal of impulses, lust--the feeling that propels the lonely out the door in search of love--has a chemical basis. It is testosterone, the hormone that creates basic sexual desire in men and women.

Researchers are now concentrating on what happens after one walks out the door and into a wide world of romantic opportunity. What physical attributes, outside the obvious, attract? What role do pheromones play? When do other, more potent brain chemicals begin to kick in? The last decade's discoveries in neuroscience let researchers predict--even, for the first time, control, albeit in a limited way--what was once thought uncontrollable: love. "We are at the dawn of a new beginning, where people may soon never have to suffer the pain of love's slings and arrows," such as rejection, difficulty in bonding and attachment disorders, says James H. Fallon, professor of anatomy and neurobiology at the University of California, Irvine, College of Medicine. In 10 years, maybe less, he says, there could be brain chemical nasal sprays to enhance love between a couple. "We're very close. And that's not just happy talk...we're like giddy kids at the possibilities."

Indeed, what scientists believe they already know about matters of the heart is remarkable. To illustrate their findings, follow the story of Mike, a fictional Everyman, as he falls in love. One night, Mike, single, nervously arrives at a party, gets a drink, then scans the room. Science tells us that, unconsciously, he is already noting the size and symmetry of the facial bones of the women around him (a recent study by University of New Mexico biologists found that symmetrical bone structure is prized more than anything because it suggests a lack of undesirable genetic mutations). He also studies the women's curves, as research shows that men prefer waists to be 60-80 percent the size of hips, an indicator, however crude, of health and fertility. (Women, for their part, seek men with slightly feminized faces--think Leonardo DiCaprio--because they appear warmer, kinder and more trustworthy.) "Judging beauty has a strong evolutionary component," says University of Texas at Austin professor of psychology Devendra Singh. "You're looking at another person and figuring out whether you want your children to carry that person's genes."

At the party, Mike subconsciously follows these clues and makes eye contact with a woman, Sue. She smiles. His midbrain--the part that controls visual and auditory reflexes--releases the eurotransmitter dopamine, a brain chemical that gives him a rush--and the motivation to initiate conversation. As he nears, Mike's pheromones reach Sue's hypothalamus, eliciting a "yes, come closer" look. Why this happens isn't clear, but one study at the University of Bern, in Switzerland, suggests that people use smell as a possible cue for distinguishing genetic similarity in a potential partner--a consideration in preventing possible birth defects.

Mike is now feeling the first flutter of sexual attraction. His hypothalamus--the brain region that triggers the chemicals responsible for emotion--tells his body to send out attraction signals: His pupils dilate; his heart pumps harder so that his face flushes; he sweats slightly, which gives his skin a warm glow; glands in his scalp release oil to create extra shine. By night's end, he gets her phone number. The next day, memories of Sue direct his brain to secrete increasing levels of dopamine, creating feelings of yearning that propel him toward the phone. He calls. She sounds excited. The dopamine released in the base of the forebrain prompts the first strong feelings of pleasure that Mike associates with Sue.

When they meet the next night at a restaurant, his stomach does flip-flops and he starts feeling giddy at the sight of her. He can think of nothing but that face, those eyes, that smile, as his brain pathways become intoxicated with elevated levels of dopamine, norepinephrine (another neurotransmitter) and, particularly, phenylethylamine (PEA). This cocktail of natural chemicals gives Mike a slight buzz, as if he had taken a very low dose of amphetamines (or a large dose of chocolate, another source of PEA). This contributes to the almost irrational feelings of attraction--we've all felt them--that begin dominating his thoughts at work, while he drives, as he goes to sleep. "It's a natural high," says Anthony Walsh, professor of criminology at Boise State University and author of The Science of Love: Understanding Love and Its Effects on Mind and Body. "Your pupils dilate, your heart pumps, you sweat--it's the same reaction you'd have if you were afraid or angry. It's the fight-or-flight mechanism, except you don't want to fight or flee."

In the weeks that follow, Mike and Sue's relationship deepens. The first night Mike brings Sue home, he dims the lights and plays a little soft music. The chemical oxytocin floods his body. Twenty years ago, oxytocin was considered a female hormone useful only as a trigger for labor contractions and to induce lactation. In the '80s, research found that it is produced in the hypothalamus by both men and women, helping to create feelings of caring and warmth (thus bonding mother and baby after birth and during nursing). As Sue's oxytocin also surges, the couple begin forming a bond. Scientists now think that oxytocin actually strengthens the brain's receptors that produce emotions. Oxytocin increases further during touching, cuddling and other stages of sexual intimacy. It may also make it easier to evoke pleasant memories of each other while apart. Mike can think of Sue and experience, in his mind, the way she looks, feels and smells, and that will reinforce his connection to her. (Helen Fisher, a Rutgers University anthropologist, is conducting research with magnetic resonance imaging to track which parts of the brain change when someone is in love.)

Next comes the wedding. Honeymoon. Now what? Fast-forward 18 months. At this point, Mike and Sue could be at a crossroads. Science tells us that 18 months to three years after the first moment of infatuation, it's not unusual for feelings of neutrality for one's love partner to set in ("Why don't you take out the trash?" vs. "I dream about you all the time"). For many, there could be a chemical explanation. The mix of dopamine, norepinephrine and PEA is so much like a drug, say scientists, that it takes greater and greater doses to get the same buzz. So after someone has been with one person for a time, his brain stops reacting to the chemicals because it is habituated. "The brain can't maintain the revved-up status," says Walsh. "As happens with any drug, it needs more and more PEA to make the heart go pitter-patter."

Couples with attachments that are shaky for other reasons (money woes, abuse, irreconcilable differences) may part and--because the body's tolerance for PEA soon diminishes--seek someone new with whom to find the thrill of early love. More likely, however, committed couples will moveon to what science suggests is the most rewarding and enduring aspect of love. Though the same addictive rush isn't involved, ongoing physical contact, not just sex, helps produce endorphins, another brain chemical, and continued high doses of oxytocin. Endorphins calm the mind and kill anxiety. Both chemicals are like natural opiates and help stabilize the couple by inducing what famed obstetrician Michel Odent, of London's Primal Health Research Center (whose book, The Scientification of Love, will be published this year), calls "a druglike dependency."

Even in the animal world, neuroscientists had long wondered what kept prairie voles loyal to one mate while their cousins, the montane voles, were promiscuous maters. As it turned out, prairie voles are much more sensitive to the effects of oxytocin. In experiments, when those receptors are blocked, the animals' stay-at-home tendencies decline. "At present, our knowledge of neuroscience is doubling every two and a half years," says Robert Friar, professor of physiology and human sexuality at Michigan's Ferris State University. "That means that in the last two and a half years we have learned more than all prior humans about the workings of the brain." Says the University of California's Fallon: "Certainly the '90s are a blur for people in neuroscience. We all want to be up twenty-four hours a day so we don't miss a thing."

But in the end, will love's mysteries ever unravel in a laboratory? Some, like Fallon, say yes. Others, perhaps most of us lucky enough to have experienced true love, might believe--and wish--otherwise. Even in this advanced age of science, where we can transplant organs, map the human genome and clone our own offspring, we still have not come close to understanding what, exactly, ignites our spark of life, our souls, our very being. Maybe, possibly, that will remain true for the farthest reaches of love.