In the Victorian era, particular flowers or floral arrangements were used as a means of communicating feelings which could not, for various reasons, be put into words; this system of coded messages was known as the language of flowers, or floriography.
Not surprisingly, the Narcissus symbolised egotism, as well as formality, and the message: Stay as sweet as you are;
The blue violet symbolised watchfulness, faithfulness, and the message: I'll always be true; the white violet carried the coded message: Let's take a chance on happiness.
It would be interesting to know whether the violets given by Diana were white or blue!
Flowers meant to 'speak' were often presented in little posies or nosegays known as tussie-mussies.
Learn to speak the language of flowers here.