SUMMARYNorthern populations of Phragmites australis (Cav.) Trin. ex Steud. (common reed) often flower so late that the ability to produce viable seeds before winter dieback can be limited. If climate changes as predicted, the reed may becotne able to set seed further north in its range. This would have implications for the ability of reed to colonize new sites as well as for the distribution of aniraals which eat reed seeds in winter.A survey of 34 British populations in 1993 and 1994 showed that seed production is highly variable between sites, ranging from 0 to 100%. Southern and western populations tended to show the highest seed sets, although some southern populations were infertile and some northern sites set seed. Average seed weight tended to be higher in sites which showed good seed set. Seeds from sites with high average seed weight tended to germinate tnore readily.The seed-setting capability of populations w-as successfully associated with climatic conditions at the time of flowering. Howe-i-er, seed weight was not found to relate to climate, but depended on seed production anci overall plant height. Logistic regression modelling indicated that the best seed sets should occur in P. australis when: (i) August rainfall is low; (ii) the combined rainfalls of September and October are high; and (iii) the combined temperatures of these months are high. The model accounts for approximately one third of the variation in observed seed sets benveen sites, indicating that other, unmeasured, factors might also play a part in determining seed set in P. australis.At three northern populations which were studied in more detail, a number of genotypes coexisted, and legitimate pollen germination and pollen-tube growth was observed in each case. As no seed set occurred in tw-' O of these, self-incompatibility cannot explain poor seed setting.

The internal temperature of the flowers of three colour variants of winter flowering Crocus chysanthus and of C. tommasinianus were compared with ambient in the dark, and when subject to artificial horizontal illumination with daylight spectra. Illuminated flowers warmed up to 3OC above ambient. In the dark, flowers also showed slight warming. In all varieties, pollen germinated more freely at 15°C compared to 6OC, and pollen tube growth also tended to be faster at the higher temperature, although pollen growth was inhibited at 20°C. Closed flowers began to open at between 10°C and 12"C, and tended to open more rapidly at higher temperatures. We conclude that flower warming at low ambient temperatures may mediate flower opening in Crocus and allow pollination, and may stimulate pollen germination and the fertilization process. Crom has the typical attributes of 'microgreenhouse' flowers, absorbing some spectra externally, transmitting other spectra internally, trapping heat energy by reflecting inner tepal surfaces, and storing energy in large gynoecia. Of the varieties tested, white and purple flowers showed the greatest flower warming, and yellow flowers the least. Yellow flowers transmit no light of less than 500 nm, suggesting that the transmission of short wavelength light may be important in flower warming.

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SUMMARYJn brighl sunshine, temperatures within the apex of the keel of flowers of Lotus corniculatus were consistently higher in dark-keeled than in light-keeled indi\ iduals. Temperature differences may increase with higher ambient temperatures and averaged 5*7 "C at 23-2 °C ambient. In overcast conditions, no significant temperature differences between dark-keeled and light-keeled flowers were observed, or light keel temperatures were slightlygreater, ln general, temperatures within keels were lower than ambient.Within sites, dark-keeled plants showed a tendency to inhabit colder microsites than did light-keeled plants. Contrary to some earlier reports, we believe that most clina! \'ariation for keel colour is temperature related.We suggest that there may be an optimum temperature for pollen germination and pollen tube growth, ln cold microsites, dark-keeled plants would be more fecund, but in warm microsites light-keeled plants would set more seed, thus maintaining the polymorphism found in most sites.