True. But then, if we want to talk about the banana tree's part individually (though all), we use *each* and not *every*. 

[BBC][1] clarifies it-

> We tend to use each if we are thinking about members of a group individually, and every if we are thinking of them in total. 

Compare the following:

> We gave **each child** who came to the party a present. We handed them out *one by one*. <br/> We gave **every child** who came to the party a present We gave **them all** a present. 


  [1]: http://www.bbc.co.uk/worldservice/learningenglish/grammar/learnit/learnitv110.shtml