. The Canadian field-naturalist. 1972 Kevan: Heliotropism in Arctic Flowers 100 r- 0-âO O O-O-O O â O O- 43. 00 02 SOLAR TIME, HOURS Figure 2. Per cent of flowers of Dryas integrifolia and Papover radicatum showing various orientations to the sun throughout a day (composite of counts of several days observations). For clarity only four of the eight categories scored in D. integrifolia are shown. Heavy open circles and solid line, P. radicatum. Large solid circles and solid line, D. integrifolia facing directly to sun (0°). Small solid circles and solid line, D. integrifolia at 45° to sun. Sm
. The Canadian field-naturalist. 1972 Kevan: Heliotropism in Arctic Flowers 100 r- 0-âO O O-O-O O â O O- 43. 00 02 SOLAR TIME, HOURS Figure 2. Per cent of flowers of Dryas integrifolia and Papover radicatum showing various orientations to the sun throughout a day (composite of counts of several days observations). For clarity only four of the eight categories scored in D. integrifolia are shown. Heavy open circles and solid line, P. radicatum. Large solid circles and solid line, D. integrifolia facing directly to sun (0°). Small solid circles and solid line, D. integrifolia at 45° to sun. Small open circles and broken line, D. integrifolia at 315° to sun. Large open circles and dotted lines, D. integrifolia at 270° to sun. tions to the sun are noticeable, and in wind the blooms are blown about. I (Kevan 1970) made a detailed study of the temperature in flowers in the high arctic and related it to pollination biology. I found the mean temperatures in heliotropic flowers of Dryas integrifolia were about 3°C above the mean ambient air temperature (9°C) while those pointing away from the sun only about 1°C above ambient. On other occasions I found heliotropic flowers had mean temperature eleva- tions above ambient of about 6°C and 7°C. Similar results were obtained for Papaver radi- catum. Results on intral-floral temperatures of the Composites Taraxacum and Erigeron (Kevan 1970) suggest that M. ambigua and S. congestus also develop temperature excesses in direct sunlight. The signifance of heliotropism to plants can be understood in the arctic environment with its low heat budget. The rates of metabolism of heliotropic flowers and inflorescences must be increased by solar warming for prolonged periods relative to non-heliotropic ones. Prob- ably pollen tube growth and ovule development are hastened and increase the chance of suc- cessful seed-set. Also the ameliorated thermal regime in flowers may act as a mechanism for holding and attracti
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