Jem and Scout decide to leave a note for Boo Radley thanking him for the objects he has been leaving them. When Jem finds that the knothole in the tree has been filled with cement, he confronts Mr. Radley. Mr. Radley tells Jem that the tree is dying, but Jem doesn't believe him. He begins to suspect that Mr. Radley wants to keep the kids from communicating with Boo. When Jem asks Atticus if the tree is dying and Atticus tell him no, Jem realizes that his suspicious are true.
Jem's crying is significant because it is a defining moment when he begins to mature and not think of only himself. He cries for Boo Radley. Jem feels sorry for him because he understands how lonely Boo must feel. He also finally realizes that Boo’s seclusion is enforced by his family and that Boo’s family must be embarrassed or ashamed of him, something that Jem is unfamiliar with because Atticus is a supportive and caring father.