It's probably an ancient desire to preserve what is precious and beautiful --yet fleeting -- that led to the practice of drying and preserving flowers. Today when we press a flower in a book, or hang roses upside down to dry, we're using techniques going back to ancient Egypt and Greece.
Later, artisans discovered that using desiccants (drying agents like borax, silica gel or even sand) could stop the flowers petals from shrinking while they dried, resulting in a much more natural look. Both of these techniques are still widely used today. Unfortunately, these techniques have a serious shortcoming -- they create a fragile end result. The flowers become quite delicate, shattering or breaking easily. Nevertheless, these techniques are still useful for certain special preservation situations when the right technology is applied.
As in most things, modern technology has come to the rescue with a marvelous technique known as freeze drying and treatments applied to the flowers prior to freezing (water-based, non-hazardous, and biodegradable!) that produces an end product that is amazingly like the fresh flower. The pretreatment helps retain color, shatterproofs and softens the freeze-dried flower.