In To Kill a Mockingbird, what is the significance of Jem crying in Chapter 7?

Jem's tears probably fell for several reasons in Chapter 7
of To Kill a Mockingbird, but they all had to do with Mr. Nathan
Radley cementing the knothole in the tree that held his secret hiding place. Jem and
Scout had been receiving mysterious gifts in the knothole of the Radley tree, but one
day on his way to school, Jem noticed that the knothole was filled with cement. When he
asked Mr. Radley, Boo's brother told him that the

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"Tree's dying. You plug 'em with cement when
they're sick."

But when Jem
asked Atticus about the tree, Atticus told him that it looked perfectly healthy. Jem was
crying because he had been lied to; because his contact with Boo had been silenced; and
because Mr. Radley had done it out of plain meanness.