How are fruit/ leaves made?

I know they grow on trees and what not, but how exactly does a tree make it's fruit? Where does the stuff come from (in the trunk). How does a tree say "Hey, I don't want this __________, so let's expel it."



Same with leaves.

How does it start making it? Are the ingredients for the fruit/ leaves already in the trunk and it just starts growing on the outside?

How are fruit/ leaves made?
Well, its a long process to explain, but in short fruits are swollen and juicy wall of ovary. Female part of modern day flowering plants have the ovules covered inside leaf like ovary. After pollens have fertilized ovules it triggers enlargement of ovarian wall leading to the formation of fruit. However, there are various modifications of such a generalization.

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