Read the poem and answer the question that follows.

I saw three witches

That bowed down like barley,

And took to their brooms 'neath a louring sky,

And, mounting a storm-cloud,

Aloft on its margin,

Stood black in the silver as up they did fly.

I saw three witches

That mocked the poor sparrows

They carried in cages of wicker along,

Till a hawk from his eyrie

Swooped down like an arrow,

And smote on the cages, and ended their song.

I saw three witches

That sailed in a shallop,

All turning their heads with a truculent smile,

Till a bank of green osiers

Concealed their grim faces,

Though I heard them lamenting for many a mile.

I saw three witches

Asleep in a valley,

Their heads in a row, like stones in a flood,

Till the moon, creeping upward,

Looked white through the valley,

And turned them to bushes in bright scarlet bud.

Walter de la Mare is the author of this poem; it was published in 1922 in a book of fairly tales.

What does the line "bowed down like barley" mean in the second line of the poem?