Oh, when she was sad, she cast herself down into such a pure depth, Even a father could not find her: Scraping her cheek against straw; Stirring the clearest water.
The second stanza transitions to a different aspect of the speaker's remembrance of Jane: her sadness.
Starting the stanza with the emphatic, "Oh," helps to signal this transition from remembering Jane happy in her thoughts to remembering her in the depths of sadness.
By using the phrase, "she cast herself down into such a pure depth," it almost makes it sound as if she took an active role—as if she willing plunged herself into the "pure depth" of her sadness.
It sounds like she embraced her sadness, accepted it as a part of her life to be considered and explored just as much as the other thoughts she delighted in.
She lost herself in this sadness. She disappeared into it. No one could reach her.
Roethke's choice of the word "father" accomplishes a couple significant things.
It introduces a familial element into the poem. Is this speaker Jane's father? Hmm…
Also, partly because Roethke chose the article "a" rather than the possessive pronoun her, "a father" also brings to mind fatheras in priest. This gives us the sense that, in sadness, Jane was not only beyond the reach of family and loved ones, but also beyond even the reach of religion, or God.
We're talking some serious sadness here.
The next two lines function as an imagistic description of her sadness. You guessed it—more nature imagery.
The speaker describes her "scraping her cheek against straw." This doesn't strike Shmoop as a typical behavior for a sad, young woman.
It sounds more like the action of a sick, or sad, animal. Maybe you've seen a dog or cat or even a horse that is having some problem or discomfort in the ears or head, they will rub their head on the ground to deal with it, perhaps as a way to comfort themselves.
The next description is a little puzzling. The speaker describes her, "stirring the clearest water." Clear water sounds pretty nice, right? But we are talking about sadness here. So, what gives?
One way to read this line is to consider the action and the consequence in a natural setting.
Let's imagine a pool of clear water, a pond or a lake. The water is so clear that we can see right to the bottom. Now, what happens if we start stirring that clear water? Yup, it stirs up all that stuff on the bottom and it isn't so nice and clear anymore.
Her sadness muddies even the purest, most pristine waters of the world. It darkens everything. Like we said, serious sadness.