Reproductive and Vegetative Performance in Two Winter Annual Grasses, Catapodium Rigidum (L.) C.E. Hubbard and C. Marinum(l.) C. E. Hubbard

Summary Demographic analysis of the leaf population of three populations of Catapodium rigidum and one of C. marinum grown throughout their life‐cycles in a growth‐room showed that the factors affecting the age‐structure and life‐expectancies of the leaf‐populations were in the order, temperature and/or photoperiod > soil‐type > populations. Winter conditions produced an uneven‐aged, long‐lived leaf population, in which maximum leaf‐age was c. 150 d. Summer conditions produced even‐ aged, short‐lived populations in which maximum leaf‐ age was c. 60 d. Leaves which developed in winter conditions had shorter expectancies in summer conditions than those which developed during summer. There were some significant differences between soils for parts but not the whole of the life‐ cycle. The result of late sowing was to reduce the differences in age‐structure and expectancies between stage of the life‐cycle and to reduce maximum leaf‐age by c. 35%. Differences between the leaf‐populations of the early‐and late‐ sown plants were apparently due to external and not ontogenetic factors. The relationship between leaf life‐expectancy and leaf and tiller numbers on the one hand and numbers and weights of caryopses on the other was investigated using a step‐wise multiple regression technique. Leaf life expectancy, especially late in the life‐cycle, was significantly (negatively) associated with caryopsis weights but not with numbers and it accounted for c. 80% of the variation. Leaf numbers, especially late in the life‐cycle, were significantly positively associated with caryopsis‐numbers and accounted for 100% of the variation. Leaf‐numbers early in the life‐cycle were also associated (negatively) with caryopsis‐weights, when they accounted for c. 40% of the variation. Tiller‐numbers were not as closely associated with caryopsis production and accounted for < 40 % only of the variation. Possible effects on seed production of alterations in the demographic parameters of leaf‐populations are discussed.