THE REPRODUCTIVE CAPACITY OF JUNCUS SQUARROSUS

S ummary The six attributes which govern the reproductive capacity of Juncus squarrosus have been measured in plants from a variety of habitats at different altitudes, mainly in an area of moorland at the head of Teesdale in the north Pennines. It was found that about eighty inflorescences per square metre were produced, but this number was reduced in adverse conditions such as at high altitudes in unfavourable seasons, or when there was a spring drought. The average number of florets per inflorescence varied from about six on well‐drained sites and at high altitudes to twenty‐two in moist conditions at lower levels. Up to 60% of the florets ripened into capsules, but in 1962, a very poor summer, less than 10% ripened at 550 m, and in 1963 only 19% ripened at 700 m. Altitude and the seasonal climate also had a marked effect on the number of seeds per capsule, and their viability. In good conditions fifty seeds developed per capsule, and viability approached 100%, but in 1962 at all altitudes, and in 1963 at high levels, values were much lower than this. Normally most of the seeds produced are dispersed, but close to the limit of capsule maturation the capsules may never open. The total number of viable seeds dispersed was estimated. Even in 1962 about 150 viable seeds per m 2 were dispersed at 550 m, and in 1963 the figures varied between 2000 and 13,500 seeds per m 2 , according to the soil conditions. At the lower levels more seeds may be produced but this is counterbalanced by losses caused by larvae of the moth Coleophora alticolella .