At the beginning of Chapter 7 of To Kill a Mockingbird, Jem tells Scout that when he went back to get his pants, they had been sewn and folded. Later, both children find objects in the tree on Mr. Radley's property. There is no overt indication about who fixed Jem's pants and who had been leaving things in the tree. Jem and Scout have guesses but can't be sure. This chapter shows Jem maturing and really thinking about what goes on around him. When the tree is plugged up, Jem is bold enough to ask Mr. Radley (who had shot at him, thinking he was a thief, in Chapter 6) if he cemented the tree.
Again, although not overt, the cementing of the tree is a parallel to Boo Radley. Mr. Radley had also shut Boo up mentally which contributed to Boo's voluntary imprisonment in the Radley house. The reader might intuit that Boo had fixed Jem's pants and planted the objects in the tree. Prior to this chapter, Boo was portrayed (at least by the children) as an outcast, even as a monster. By the end of the chapter, there is at least the suggestion that Boo has been misunderstood.
Near the end of the chapter, Scout senses that Jem knows something but is not telling. It is evident that Jem has an idea about who has been leaving things in the tree and who fixed his pants.
He had been on the verge of telling me something all evening; his face would brighten and he would lean toward me, then he would change his mind. He changed it again. “Oh, nothin‘.” (Chapter 7)