"From the very fountain of enchantment there arises a taste of bitterness to spread anguish amongst the flowers"

Lucretius is revealing the idea that even the most stunning and enjoyable things in life can in some cases be tainted by a sense of unhappiness or bitterness. The "fountain of enchantment" might refer to anything that brings happiness or joy, whether it be love, friendship, or beauty. However, this delight is often short lived or overshadowed by negative emotions, which can "spread anguish amongst the flowers" - simply put, ruin the charm of the scenario. This quote is a tip that life has lots of ups and downs, which even the very best of times can come with their own troubles.