I expect that white mass is mold. The cut flowers don't last long and the water soaked dead stems and the "flower food" (for cut flowers?) which usually contains some kind of glucose probably served as ideal growing medium.
Î¥ou might be able to get your flowers to last a little longer -- Take the flowers out and discard and thoroughly clean the vase. If the flowers above those stems are still alive, take them out and cut the bottoms of the stems off all the way to solid, green undamaged stem, then rinse in clean water with some hydrogen peroxide or alcohol in it. Put in a vase of fresh water. If the flowers are too short for this vase now, find another one that works better.
If the center of the flower has turned brown, that one is a goner even if the petals still look good. No point in trying to save it, and the fungus in the stem will contaminate the new vase.
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