What did Darwin mean by "degraded flowers"?
Perfect flowers have both male and female parts.
"Degraded" isn't used anymore - just "imperfect".

"A bisexual (or “perfect”) flower has both stamens and carpels, and a unisexual (or “imperfect”) flower either lacks stamens (and is called carpellate) or lacks carpels (and is called staminate). Species with both staminate flowers and carpellate flowers on the same plant (e.g., corn) are monoecious..."

ref https://www.britannica.com/science/perfect-flower

Found by searching for "perfect flower"