Fig. 3. Total tiller number (a) and number of tillers shorter than 4 cm (b) during regrowth of perennial ryegrass swards from 21 July to 15 Sept. 1997 at ambient (36 Pa) and elevated (60 Pa) pCO₂ and after an infrequent (4 cuts yr^-1) and frequent (8 cuts yr^-1) cutting treatment before the beginning of the experiment (Error bars = SE, n = 6).