About "Mariana"

[white camellia]

The underlined lines in the following excerpt from Tennyson's "Mariana" escaped me. Any help?

About a stone-cast from the wall
A sluice with blacken'd waters slept,
And o'er it many, round and small,
The cluster'd marish-mosses crept.
Hard by a poplar shook alway,
All silver-green with gnarled bark:
For leagues no other tree did mark
The level waste, the rounding gray.
She only said, "My life is dreary,
He cometh not," she said;
She said, "I am aweary, aweary,
I would that I were dead!"

And ever when the moon was low,
And the shrill winds were up and away,
In the white curtain, to and fro,
She saw the gusty shadow sway.
But when the moon was very low,
And wild winds bound within their cell,
The shadow of the poplar fell
Upon her bed, across her brow.
She only said, "The night is dreary,
He cometh not," she said;
She said, "I am aweary, aweary,
I would that I were dead!"

[L.M. The Third]

How do they escape you? Do you not understand the words, or the significance?

[white camellia]

I understand it as a poem in a way, but I have difficulties simply with those particular lines. I can read and understand the rest.

[Albion]

Hard by a poplar shook alway,
Nearby, a Poplar (a type of tree) rustled its leaves all the time

All silver-green with gnarled bark:
It was siver green (in colour) with a knobbly bark

For leagues no other tree did mark
For many miles (league= old and poetic unit of distance of
variously 3 or 7 miles) no other tree was present

The level waste, the rounding gray.
On the even (flat) ground in that neighbourhood in the greying (fading) light of evening

And wild winds bound within their cell,
And the normally wild winds were calm contained within their source (ie not blowing)