"There are still the flowers to buy." (pg. 9); "Mrs. Dalloway said something (what?), and got the flowers herself." (pg. 29); "Mrs. Dalloway said she would buy the flowers herself." (pg. 37)
Here the reader sees the first sentence of the first three sections of The Hours. Each one begins with a different women with a sort of variation on the famous first line of Mrs. Dalloway-- Clarissa Vaughn thinking of her own flowers and thus establishing her as the modern day Clarissa Dalloway, VIrginia Woolf struggling to write the iconic line that defines the entire book and Laura Brown reading said line in her 50's bedroom. Cunningham uses that line to first tie all three women together. He also uses that line as a inside joke of sorts with those readers who have also read Mrs. Dalloway. The Hours deals so heavily with the themes and effects of Virginia's novel that it only fits that he would tie the book into his own piece of fiction in every way he could.