Answer:
Of the forest's ferny floor
Explanation:
<em>Alliteration</em> is the repetition of the same sound at the beginning of words occuring in close succession.
The last line is the best example of alliteration as it contains three successive words beginning with f:
Of the forest's ferny floor.
Technically speaking, two more lines contain some alliteration:
"Is there anybody there?" said the Traveler,
and
"And his horse in the silence champed the grass".
However, these cases of alliteration are hardly noticeable while alliteration in the line "Of the forest's ferny floor" really works and makes it much more memorable.
