Concentrations of crystalline cellulose and lignin in sections of the elongating maize internode. Cellulose (% by weight) was assayed using the acetic acid/nitric acid method of Updegraff  from three biological replicates. Lignin was assayed after the AIR was hydrolysed with 25% acetyl bromide in acetic acid and the residual lignin materials were weighed on filter paper and absorbance measured at 280 nm (Hatfield et al.) . The data are means of three biological replicates and standard errors are indicated. Lignin was not measured in Sections S1, S3, S5, S7 or S9.