A combined field and growth-room experiment was carried out using three populations of Catapodium rigidutn and one of C. marinum grown reciprocally on the soils and at the sites where they occurred and also at sites where neither species occurred naturally. The effect of late emergence on vegetative and reproductive production was also investigated. No plants survived to mature seed on either of the acidic soils in the field and on only one in the growth-room.

The coastal site was most favourable with least mortality, more vegetative growth in winter, most production and earlier maturation of caryopses. At two of the three sites when there were indigenous and artificially established colonies of the same populations, the indigenous plants were the most productive. Significant differences in productivity between sites were correlated with differences in the level of nutrients at the various sites. No differences between the populations at any one site were detected. There were, however, significant differences in the components of yield between the populations when all the sites were taken together. There were significant differences in the production of caryopses between the replicate colonies of each population at a particular site. The marked heterogeneity within sites indicated by this was probably the reason for failure to obtain evidence for adaptation to a particular site by its indigenous population. Constraints on the production of caryopses in the field operated through caryopsis number and not weight and probably early in the life cycle, since the number of tillers and the number of spikelets per inflorescence were the components of yield most reduced in the field compared with the equivalent treatments in the growth-room. The results of the growth-room experiment showed that soil factors and not genetic differences between populations were the main determinants of differences in reproductive performance between sites. There were, however, some significant differences in phenology, vegetative growth and yield of caryopses, between the populations of Crigidutn and between these and the one of C. marinum. The effect of late sowing in the growth room was to shorten the life-cycle, to reduce the production of caryopses slightly, to increase the variation within treatments and to reduce the effect of soil type on performance.