The amounts of dry matter, mobile carbohydrate and reserve carbohydrate have been determined in bracken fronds and buds, frond-bearing rhizomes and storage rhizomes over a period of 13 months. Dry matter and reserve carbohydrate levels are closely linked, especially in the rhizomes, falling from May to the beginning of July and rising until complete frond death at the end of September; but variations occur between frond-bearing and storage rhizomes. The carbohydrate reserve of frond-bearing rhizome is rapidly exhausted by the developing fronds and further carbohydrate is drawn from the storage rhizomes, but a concurrent fall in mobile carbohydrate suggests that the rate of conversion of reserve carbohydrate is slower than the rate of translocation to the fronds. By August, there is an accumulation of carbohydrate in the frond-bearing rhizome, which is followed by a fall in September and this again suggests low enzyme activity in the storage rhizome, but also that sink strengths in bracken are in the order (1) developing buds, (2) storage rhizome, (3) frond-bearing rhizome.

The responses of bracken to cutting and herbicide-application are discussed in relation to sink strengths and a low level of enzyme activity in the storage rhizome.