Sweet violets have always been my favorite spring flowers, maybe because they are my mom's too. When I was a little girl, she would always sing me this beautiful Romanian love song, "Sweet violets for the girls". As the song says, violets are for the girls, from their lovers. A gypsy flower girl picks them up from a wonderful garden and she encourages men to make up with their sweethearts with a sweet violet bouquet.
In her secret closet, among high-heel shoes from her youth, purses, nice clothes and jewelery, my mom had a small bottle of sweet violet perfume, a few sweet violet scented soaps and a fake bouquet of sweet violets. I loved peeking in her closet, from which a divine sweet violets scent embraced me every time I would open the door. As you may have guessed, the first thing I did was to try on her shoes, even when I was too little and they didn't fit - maybe because of that they got ruined without mom wearing them! I also enjoyed smelling the soaps and taming the back of my ear with perfume; then I would gently open mom's jewelery box and take a quick look - I was never too fond of jewels. After checking into every purse, I would take the shoes down, then smell the perfume and soap again, before leaving the secret closet. One day, Mom took the fake sweet violets bouquet outside and put it in a small vase she just bought, in her bedroom. Every spring, she would replace it with a real bouquet, which she bought from a gypsy flower girl in our neighborhood. Actually, many flower girls were out on the streets on those days, with their wicker baskets, full of small sweet violet bouquets, same as Eliza Doolittle in "My Fair Lady".
Later in life, I bought sweet violets for myself in the spring and put them in a special vase I saved especially for spring flowers. After my kids were born and I began walking in the park more often, I learned every place where sweet violets grew and every spring I would check on them to see if they were starting to bloom. It was such a joy to pick up a few for my vase, every day! My children also enjoyed picking sweet violets growing in the park, which were more than plentiful; in fact they were invading the lawns.
Viola odorata, the sweet violet everyone knows, is an invasive plant and some call it a weed because it grows wild in the woods or under the trees in the park. Nevertheless, the so-called weed has been very much appreciated for its sweet fragrance since old times. The Greeks used them to perfume wine, while later, Napoleon chose sweet violet as his signature flower. But the most important use of this delicate plant has been fragrance extraction from their scented flowers. Ionone is the aroma compound which Viola odorata contains in its flowers. It has the property to turn off the ability of humans to smell the fragrant compound at a time. You can smell sweet violets and sense their scent, but on the next second they won't smell anymore - hence, you cannot sense their scent anymore because the ionones are blocking your smell sense. Ionones are present in most of essential oil such as rose oil. Their discovery in 1893 was revolutionary for the modern day pefumery because synthetic ionones could then substitute the very expensive natural violet ionones.
Sweet violets have been cultivated for commercial purposes since old times, but reached their highest peak during the 19th century when the demand was far greater than the offer. This was the time when new cultivars were created from the famous Parma Violet, from which later was created the Violet of Toulouse. Both species have double flowers and also double fragrance. Parma Violets are not hardy in cold winter climates and aren't known to grow in the wild as their wild relative, the Sweet violet. Their double flowers and leaves resemble to those of the African violet, but there is no connection between the two species. It is supposed that Parma violet might be descendant of Viola alba, native to southern and central Europe and Mediteranean. Violet of Toulouse, a very fragrant, hardy winter and double-purple flower, was prefered to Parma Violet during the years and is now cultivated especially for cut flowers in Toulouse, France. A whole industry flourished based on this beautiful flower, from perfumery to bakery and confectionery. Most of the famous perfumes producers are using its fragrance.  The town of Toulouse celebrates Violets Day every year in February, during the violets' full-blooming season. Many tourists are visiting the "Pink City" - as Toulouse is called - and enjoy the products made of the Violets of Toulouse. 
In my earliest years as a gardener, I had sweet violets in my block's garden, with white and violet flowers. They grew wild there and survived for many years, while the garden was neglected.
It was a joy to watch them grow, but I much more preferred to buy some from the flower girls than rip them out from my garden.
I brought both species of sweet violets with me when I moved into my house in the village. They are now growing in my garden. Every spring I like to take some of those sweet blooms and put them in my vase. They are somehow crowded between the mums and asters, so they can't invade the garden, as they usually do elsewhere - not that I wouldn't like that, but I just forget to move them from there to another location, where they would be able to invade, thus making more flowers, to my delight. However, I now have a four year old grandchild, who loves picking up flowers from my garden and offer them to his mom. And I let him - moreover, I encourage him to pick them up. He also enjoys gardening with me so this spring, as soon as the sweet violets will stop blooming, we might just move them together. We need more sweet violets for the girls in our family!
 - http://www.csmonitor.com/The-Culture/Gardening/2009/0227/the-very-fragrant-parma-violet
 - http://www.cosmeticsbusiness.com/technical/article_page/Fragrance_The_sweetness_of_violets/46761
 - http://www.france-voyage.com/tourism/violet-toulouse-882.htm