Pollen Release in the Common Ragweed (Ambrosia artemisiifolia)

Abstract

1. A study of staminate flowers of common ragweed (Ambrosia artemisiifolia L.) revealed six more or less defined stages, which are described: (a) maturation of the flower; (b) extension of pollen sacs; (c) opening of pollen sacs and dropping of pollen clumps; (d) flotation of pollen by wind; (e) extension of the pistillodium; and (f) closure of the flower. Stages b and c were examined in relation to environmental factors-temperature, humidity, light, and water availability. 2. Actual pollen release is accomplished mainly by enlargement of the filaments of the stamens which extends the pollen sacs and pushes open the corolla lobes, and by dehiscence of the sacs by pleating and separation of their walls and extension of the anther appendages. The pistillodium may function as a "sweeper" of pollen grains still remaining in the anthers. 3. Field studies showed the occurrence of a definite diurnal periodicity: extension and opening of the anthers occurs between 6:30 and 8:00 A.M. This is correlated with rise in temperature and reduction of relative humidity. 4. Experimental studies on excised flowers and whole plants confirmed that the opening of flowers is controllable by regulating the temperature and relative humidity. The extension of anthers was slowed or prevented by holding the flowers at reduced temperatures. The opening of pollen sacs was retarded or stopped by high humidity. Both types of inhibition were reversible under the conditions of the experiments. Alterations in the amount of light and water failed to induce significant changes.