What's the difference between barken and birken?

Barken

Definition:

• (a.) Made of bark.

Example Sentences:

Birken

Definition:

• (v. t.) To whip with a birch or rod.
• (a.) Birchen; as, birken groves.

Example Sentences:

• (1) The alpha subunit comprises 92 amino acids, of which 6 are Lys residues (Morgan, F.G., Birken, S., and Canfield, R.E.
• (2) Leu in the common positions (12, 15, 19, and 22) has also been found in human choriogonadotropin pre-alpha subunit [Birken, S., Fetherston, J., Desmond, J., Canfield, R. & Boime, I.