What are some citations from the novel To Kill a Mockingbird that show Jem's loss of innocence?

JEM AND NATHAN RADLEY.  One
of Jem's earliest discoveries about adult deceit comes when he discovers Boo's brother
cementing their secret knothole. Nathan tells Jem that the tree is diseased, his reason
for the use of the cement. When Jem questions Atticus, Atticus tells him to look for
himself: The tree is perfectly healthy, he tells Jem, who immediately realizes that
Atticus is being straight with him and that Nathan has lied. He has sealed the knothole
only to prevent further communication with
Boo.

JEM AND THE LYNCH MOB. 
Jem discovers that some of Maycomb's citizens are not the "best in the world." Though
Jem may not have understood the group's true intentions, he did recognize that they
would have harmed Atticus if necessary.

JEM
AND THE JURY.  Jem is distraught following the guilty verdict. He
recognized that Atticus proved his case and that Tom could not have been guilty. The
jury's guilty verdict makes Jem wonder about the jury system as well as the goodness of
his neighbors in Maycomb.