Carboxyl groups have an electronegative oxygen atom double bonded to a carbon atom. This carbon-oxygen bond is very polar and the fact that its a double bond increases the polarity of the bond.
PEA agar, also referred to as Phenylethyl Alcohol Agar is a medium  used by microbiologists to grow microorganisms. The ingredient that  supplies nitrogen is casein. Making the world better, one answer at a time.
A by-product of cotton manufacturing, cottonseed meal as a fertilizer for the garden is slow release and acidic. Cottonseed meal varies in formulation slightly, but is generally made up of 7% nitrogen, 3% P2O5, and 2% K2O.