Once the pumpkin starts growing, the flower is no longer needed. The pumpkin keeps growing.
It works like this... the plant grows... next it sprouts flowers... next wind or bees pollinate the flower... next flowers fall off and turn into tiny little pumpkins... then grow to maturity. If the flowers do not get pollenated, if extreme heat of some kind, plant disease or fungus is exposed to flower can kill flower and the pumkin will not develop.
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