Study of the growth of an undefoliated stand of Italian ryegrass showed that the yields of leaf blade, leaf sheath, and dead matter remained fairly constant for 10 weeks in winter, although individual tillers produced a new leaf every 16–19 days. From these data it is estimated that approximately 8 lb. of dry matter/acre/day was lost through the death and subsequent decomposition of plant tissue.Investigation of the recovery growth of a closely defoliated perennial ryegrass sward in summer showed that the yields of leaf blade and leaf sheath increased rapidly with time until there was sufficient foliage to intercept virtually all of the noon light and slowly thereafter; whereas the yield of senescent and dead material increased slowly at first and rapidly later. It is suggested that the rate at which dry matter accumulated beyond the stage of complete light interception depended to a large extent upon the rate of tissue decay.Determinations of the composition of the stubble of a perennial ryegrass sward which was leniently defoliated at weekly intervals in late summer showed that the proportion of leaf blade in the material necessary to intercept 90–95% of the noon light decreased with time, whilst the proportion of dead matter increased. It is pointed out that the rate of dry‐matter accumulation was probably affected throughout by factors which determined the rate of decomposition of dead material. The conclusion drawn is that pasture production is likely to be good only when grazing or cutting management ensures that dry‐matter losses by decay are kept to a minimum, whilst gains by photosynthesis continue at a high level. The results of some cutting trials are discussed in thes