Langston Hughes, in his poem The Negro Mother, uses a few different poetic devices.
A simile is a comparison made between two typically different things using the word "like" or "as" to make the comparison.
A simile is found in both lines five and six:
Look at my face -- dark as the night --
Yet shining like the sun
The first comparison made is between the speaker's face and the dark night. The second comparison is made, again, to the speaker's face, but this time it is compared to the sun.
These two comparisons combine to create a paradox. A paradox is a statement that is made which seems contradictory to itself. Here, the paradox is that the speaker's face can be both dark as night and shining as the sun.
One last poetic device used in the poem is alliteration. Alliteration is the repetition of a consonant sound within a line of poetry. Therefore, the repetition of the "c" in line ten is defined as alliteration.
Bringing the cotton and the corn to yield.