Final answer:
The sound device in the lines is alliteration, which contributes to the poem's mournful mood.
Step-by-step explanation:
The sound device in the lines is alliteration. Alliteration is the repetition of consonant sounds at the beginning of words. In this case, the repetition of the 'w' sound in 'withered vines' and 'withered leaves' creates a soft and mournful mood. It emphasizes the desolate and barren nature of the setting, contributing to the overall melancholic tone of the poem.
Learn more about sound devices in poetry