. The Canadian field-naturalist. Heliotropism in some Arctic Flowers' Peter G. Kevan' Department of Entomology, University of Alberta, Edmonton, Alberta, Canada. Abstract. Heliotropism is described for the flowers of four species of arctic plants. Only one, Papaver radi- catum is heliotropic throughout the 24 hours of sun. The others, Dryas integrifolia, Matricaria ambigua, and Senecio congestus are heliotropic for several hours centered about solar noon. Heliotropism is abolished in cloudy vs^eather. The significance of heliotropism is discussed in relation to intra-floral temperatures and re
. The Canadian field-naturalist. Heliotropism in some Arctic Flowers' Peter G. Kevan' Department of Entomology, University of Alberta, Edmonton, Alberta, Canada. Abstract. Heliotropism is described for the flowers of four species of arctic plants. Only one, Papaver radi- catum is heliotropic throughout the 24 hours of sun. The others, Dryas integrifolia, Matricaria ambigua, and Senecio congestus are heliotropic for several hours centered about solar noon. Heliotropism is abolished in cloudy vs^eather. The significance of heliotropism is discussed in relation to intra-floral temperatures and reproduction. Introduction Heliotropism is defined here as the diel bending response, or turning, of plants directly to and with the sun. Thus heliotropism is a form of positive phototropism. Loeb (1890) used the term heliotropism to describe what is now known as phototaxis (Fraenkel and Guim 1961) and until recently botanists have used the term interchangeably with, and to mean phototropism. Taxes are exhibited through lo- comotion, while tropisms are exhibited through curvatures of sedentary plants. Although blooms such as Helianthus and others have long been known to turn to the sun throughout the day (Hooker 1881, Wiesn- er 1879, 1882) I can find no modern compre- hensive account of this phenomenon except for two small works (Polikarnov 1954, Morozov 1963) demonstrating heliotropism in sun- flowers under field conditions. Review articles such as by Schrank (1950), Brauner (1954), Reinert (1959), Briggs (1963, 1964) and others discuss the general mechanisms of phototropism and the physiology of auxins, but do not mention heliotropism per se. Schrank (1950) and Leopold (1964) briefly mention the responses of leaves to the sun. Methods Most of the following work was carried out at Hazen Camp (81° 49' N., 71° 18' W.) on northern Ellesmere Island, At various times during several days of sunny weather in 1967 and 1968 about 1,300 flowers of Dryas ^Contribution No. 862, Pla
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