Analysis of Dow Kritt

Samuel is forever talking of his elm --
But I did not need to die to learn about roots:
I, who dug all the ditches about Spoon River.
Look at my elm!
Sprung from as good a seed as his,
Sown at the same time,
It is dying at the top:
Not from lack of life, nor fungus,
Nor destroying insect, as the sexton thinks.
Look, Samuel, where the roots have struck rock,
And can no further spread.
And all the while the top of the tree
Is tiring itself out, and dying,
Trying to grow.