1. Pure swards of S. 48 timothy and S. 215 meadow fescue were cut (a) after ear emergence, (b) before ear emergence and in the aftermath to prevent flowering, and (c) every 4 weeks. The number and weight of tillers and leaves were determined.

2. Tiller numbers declined considerably from early spring to the middle of summer. This fall was reduced by a system of frequent defoliation in the wet summer of 1956, especially in timothy.

3. Leaf weight per unit area of sward increased rapidly from early spring until about the time of ear emergence; no further significant gains were recorded after ears had appeared, when the plots were cut for hay.

4. The weight per leaf also increased in the spring and was similar in both species. In the regrowth following a cut meadow fescue produced considerably heavier leaves than timothy.

5. As both grasses approached the flowering stage, their leaf canopy was increasingly raised above ground level. Variable proportions of foliage were thus removed by cutting according to the developmental stage of the plant. Crop growth rates following a cut appeared to be related to the amount of leaf material remaining in the sward.

6. Relative growth rates during uninterrupted growth were greatest around the time of ear emergence.