In the story, Myop only lays down her flowers after she discovers the noose. Prior to this, she notices a wild, pink rose she wants to add to her collection of flowers. In the act of lifting up the rose from the soil, however, she discovers the rotted remains of a noose.
Eventually, she also discovers another piece of rope clinging to the overhanging branches of an oak tree. Both pieces of rope seem to be connected to the death of the stranger before her. It is only after the second rope discovery that Myop lays down her flowers. The symbolism of her action cannot be argued: Myop is laying down her innocence forever. The question begs to be asked: why does Myop lay down her flowers?
We can speculate that Myop may have wished to leave behind any reminder of the grim sight she has just seen. From this vantage point, her action then becomes an ironic one. If she is a sharecropper's daughter, she will have known (even at her young age) that lynchings are an extreme and unrelenting threat to her own people. No matter what she does, she can never erase the fearful memory of that devastating discovery from her mind. Thus, the act of laying down the flowers becomes an exercise in futility.
If, however, Myop has laid down her flowers as a sign of respect for the dead, her action can also be viewed as an ironic one. During the Jim Crow era, lynched men and women were often left hanging on trees as an example to others. Sometimes, large crowds gathered to view the dead body. More often than not, entire families had assembled beforehand to watch the proceedings of the lynching. Even at ten years old, Myop would presumably have been made privy to these grim facts by her parents.
So, the act of keeping the body on the tree or of neglecting to bury the body constitutes an act of grave disrespect to the victim and his family. At the end of the story, Myop lays down her flowers; perhaps we can interpret this as a mark of respect for the lynched man. If anything, though, her innocent action cannot obliterate evil; instead, it only serves to highlight the graphically violent nature of the scene before her.
If we consider the entirety of the story, it could be considered an example of situational irony that she lays down the flowers. This is only because at the beginning of the story, she is so carefree; we don't expect her to encounter a dead body and thereafter to lose her sense of innocence in being carefree. We don't expect her to make a solemn gesture of laying down the flowers.
However, if we consider the final moment when she lays down the flowers, I find this more fitting than ironic. The girl has lost her innocence. Her name "Myop" is an allusion to myopia. This is nearsightedness or being short-sighted, the latter of which can also mean lacking insight and wisdom. In this story, Myop lacks life wisdom. She doesn't yet know or understand racism and violence. Her encounter with the corpse and the remains of a noose give her an initial lesson in the cruelty and violence of racism. When she lays down her flowers, it is symbolic of a gesture for the deceased man, but it is also symbolic of her laying down her innocence. Again, this ending seems ironic compared to the beginning of the story, but the gesture itself is not ironic: it is fitting and symbolic of the change that occurs in the girl's mind.