AbstractThe relationship between the degradability, determined with a commercial cellulase preparation, of the cell walls of various plant parts of Italian ryegrass, maize and red clover can be expressed as Y = A ‐ Be−k1t‐Cek2t, where Y = percentage of cell walls degraded, t = reaction time, k1 and k2 are rates of degradation, and A, B, and C are constants where A = B + C. Degradability of the cell walls of Italian ryegrass or maize could be predicted accurately from the absorbance of the filtrate at λmax 282‐288 or 310‐324 nm. Treatment of cell walls of barley straw with 0.1 or 1M sodium hydroxide for 7 or 20 h degraded between 12 and 41% of the walls and led to the release of p‐coumaric and ferulic acids, the amount increasing with concentration of alkali and treatment time; the less concentrated alkali released more ferulic than p‐coumaric acid. Treatment with the cellulase preparation of the residues from alkali treatment showed that they were almost twice as degradable as the untreated walls.