Patterns of cellulose synthesis in excised and intact roots were also investigated by autoradiography. During short incubation periods with ¹⁴C-6-ache/MiamiImageURL/B6WFC-4DVNJ6K-55-2/0?wchp=dGLzVzz-zSkzV"" class=""charImg"" alt=""image"" title=""image"" height=""10"" width=""11"">-glucose, most of the label incorporated into the ethanol-insoluble fraction was recovered, after hydrolysis, in hexose. When this residue was extracted with alkali, the insoluble α-cellulose contained ⁴C in glucose units only. This incorporation was presumed to be related to the amount of cellulose synthesised during the incubation. Autoradiographs of sections extracted with alkali revealed, therefore, the incorporation pattern into cellulose within the root. Cellulose was synthesised only slowly in cell walls of the cap and meristematic region. As cells began to extend more rapidly, there was a sharp rise in incorporation, increasing to a maximum in the pith, inner and outer cortex and epidermis between the third and fourth mm behind the cap-junction. Cells at this stage had not completed their growth, and no direct relationship could be inferred to exist between deposition of cellulose and extension of the wall.